For Forces families particularly, boarding schools are important. If you are going to be moved every 18 months - 2 years, you have two choices.
1: The non-Forces partner stays in one place whilst you move around. This can work - we have done it on and off for 16 years; but it depends on where you are sent. We did two years of dh commuting between Brussels and Cornwall so ds could stay at prep and I could continue my career. In reality, it wasn't weekending, but ended up being six weeking, which puts a strain on a marriage. So, is divorce a better option than boarding?
2: You can move around with your Forces partner. These moves will be roughly 18 months -2 years, but you may not get much notice, say a maximum of 93 days to organise a move, a new address and a school. If you are going to be in a married quarter, you may not get the address until 1 -2 months before you move, down in some cases to a week before you move. You cannot organise a school until you have an address..the good schools will all be full, and you have to take what's left...special measures etc. You don't have a choice. You also know of course, that the Armed Forces won't move you in line with your kid's schooling - so you could be moved at the end of Year 10, or even in the middle of year 10, to the other end of the country. The appointers don't work in line with academic years or school terms, so again, disruption for the kids. Hence, boarding school is the option for many Forces families.
It goes against all my instincts as a parent and a teacher to constantly pull my ds around from one school to another, as I know how disruptive it can be.
Of course, parents carefully research their choice of school. There are certain schools that I know would not suit my ds at all; whereas I think he would slot into others very well. Just because some parents choose to board their children doesn't mean they are stupid or insensitive to their needs fgs.
As for judging those who send their kids away to school; I try not to judge those who don't have the common sense to see that for most Forces families it is a big decision, but one that has to be taken sometimes.