I think the higher number of applications is also a symptom of the system being broken.
If schools had the resources/flexibility/budget/space/time/staff to accommodate children with, let's say milder needs (I appreciate this isn't the best wording, but I can't think of what other description to use right now) - then those children may be able to manage in schools without needing an EHCP.
But because schools are stretched, underfunded, understaffed, staff are overworked and stressed, larger class sizes (Apparently now many class sizes routinely go over 30, which I always thought was the upper limit) and lots of pressure about exams (Phonics screenings, SATS, a certain number of GCSEs), school is harder and more stressful for staff and harder and more stressful and less flexible for a certain number of pupils who might have actually been fine in an environment where their teacher had time and space to differentiate for them, or notice when they needed a break and send them to run laps around the playground/go and do quiet work in the library, or get to know their slightly quirky communication style, or whatever it is that they needed. Which they may not have the time or energy to do now - hence parents need to apply for an EHCP so that these needs can be met.
Or where school management could have agreed to compromises such as it's better for them to attend for part of the week than not attend at all, or it's better for them to achieve an NVQ rather than fail a GCSE, that kind of thing.
Because you also have things which are a secondary issue such as behaviour - obviously teachers are no longer allowed to assault or humiliate pupils as a disciplinary strategy, which is good, but nobody seems to agree on what to replace it with, replacing the basic idea of punishment with token sanctions is enough of a deterrent for some pupils but not others, some schools employ the "broken windows theory" and get really strict on every little thing in pursuit of general compliance, some schools go the opposite direction and do more "cosy chat" style approaches which really needs full staff training and buy in which is often not met, or sometimes just assumes more resources than the school has. And where a school has been through several changes of leadership sometimes you also get a ping pong effect between these approaches which is even worse.
And while it's good in theory for councils and school management to try to improve things like attendance, it doesn't realistically help to simply force children back into schools without actually looking at what was causing a barrier to attendance in the first place. Many persistant truants in the past are probably kids who need EHCPs today. Truanting wasn't a solution that worked in terms of their education, but it did mean nobody had to fund any support for them.
It also used to be much easier to access things like speech therapy - if you go back about 15-20 years, I remember it being fairly common for children to be referred for speech therapy at about the age of 2 if they weren't yet talking or age 3 if their speech was behind or unclear. When DS1 (a teenager) was little the old rhetoric of "Oh don't worry they'll catch up" was being discouraged because some children don't catch up without support. So the support was fairly widely offered - not to every child, but to a sizeable minority, and most of them caught up whereas some would go on to get a diagnosis of autism or some other issue which would always affect their communication. But now there is much less screening for issues like speech, it's left up to parents to speak up if there is a problem (which they may not be aware of) and if you do have a concern then the waiting list for services like speech therapy is long. This means children are starting nursery or in some cases reception while still pre-verbal, and have gone through several years where other children were having crucial experiences interacting with each other and with adults verbally and learning from this, but the children with speech delay can't access as much of it. So they are behind, sometimes learning compensatory strategies (such as thumping the kid who took your toy) which can become unhelpfully ingrained, and by the time they do access therapy, there is more work to be done which increases the queueing time for those in line behind them. And so they are starting school with greater needs than they might have had if they had been able to access speech therapy at age 2 or 3, so they might need an EHCP, whereas they may have caught up enough to fit in with the rest of the class before.
And then we do also know that there are more children with SEND needs in mainstream schools, some because the boundaries have shifted where a SEN placement would previously be recommended (of course these children presumably would be included in stats either way so perhaps irrelevant here), and some because there is an increase in children with SEND, I understand the estimate is around 10% increase, due to a combination of better survival rates of premature babies, older age of parents and some unknown factors.
Poverty affects children's school perfomance and developmental outcomes negatively too, and child poverty has been rising over the last 10-15 years, we're now back to roughly where we were in the year 2000. This may account for some children tipping over into needing support whereas they might not have been in that category otherwise. Combined with more awareness today (the only SEND I remember in mainstream schools in the year 2000 was "learning difficulties" and maybe dyslexia and possibly ASD - no ADHD, and far less autism than is recognised today) some of the rise in applications might be related to this.