It’s because there’s no easy answer and it depends on the child.
People who potty trained early and had success will swear it’s because they did it early.
People who potty train early and it doesn’t work out will swear the child wasn’t ready
People who leave it till later and didn’t try early and have success will swear it’s because they waited till the child was older
People who left it till later and didn’t try early and struggle will say it’s because they left it too late.
Really, it’s down to the individual child and you’ll never really know how much age or “readiness” had on their journey.
I potty trained my DS at 18 months. I did this for two reasons 1) We had the Easter break and it seemed like a good time and 2) I had a friend who was still struggling to potty train her 4 year old and swore it’s because she left it too late and didn’t persist.
We had a funny potty training journey with DS. He wasn’t really showing any signs of readiness before we started (hence why I’m sceptical about how vital these are), we just thought we’d give it a go and simply stop if it was a disaster. He certainly didn’t click perfectly overnight and it took a while before he actively told us he needed the toilet, he needed help to manipulate his clothes etc, and yeah there were some accidents. But equally he was doing so well at holding his bladder for up to 2 hours at a time that his nursery felt it was a shame to stop so we powered through. No, he wasn’t accident free in a week but I think it was right for him. That said, I’ll probably wait a bit later with my second child until he has the language burst (DS had it at 20 months) as that would have been helpful.
My friend’s child did eventually get there, but was still unreliable for a year after they ditched nappies, even though she was 4. We don’t know why, she just found potty training hard despite being a bright little girl. My poor friend is now stressing out that her (now 5 yr old) daughter just simply cannot stay dry overnight. My DS randomly went completely dry overnight just before his 3rd birthday, with no input from me at all. He literally wet the bed once, on his second nappy free night, and never again. Personally I believe overnight dryness is hormone controlled and my DS just happened to be ready and my friend’s daughter will get there in her own time. My point is, we don’t know why my DS potty trained early and my friend’s DD late and we never really will.
Anyway, this is a very long winded way of saying that there’s no one answer and you just have to do what you think best based on how you feel and your child feels. Don’t panic over the 30 month thing, even if you ‘miss it’, I doubt your child will be going to university in nappies. They all get it in the end. I probably would have persevered a bit longer, but the fact you feel relieved about going back to nappies shows it was probably the right choice for you. It’s difficult to support your child properly if you’re finding it stressful, so taking a break was likely a good thing.
Deep breath OP, you’ll all get there in the end. Just trust your instinct and don’t worry too much what the books say.