Ha funnily enough our joint income is basically the same as yours, infact might even be a tad higher, few percent maybe.
But we have 2 kids 1, 4 years old we are still paying (nearly) full time childcare for (££££) and the older one is 15 and wants grown up things, and soon will be thing like driving lessons etc.
We have 2 cars, which to be fair, now we both work from home, we could probably manage on 1, but we live in a rural area so no public transport and nothing within walking distance. And because of where we live we are lucky, things like car insurance is cheap as chips, and I service the cars myself and they are not new cars, so pretty cheap apart from fuel obviously.
We dont go out to each much etc, which is even more expensive with 4. We've not been on a proper holiday for years.
But childcare, the 15 year old wanting "stuff" and using electricity, food for 4, added things like washing machine, dishwasher etc going on more. Petrol to drop kids at nursery, thankfully neither of us commute now.
We have a bit left over, but nowhere near as much as you, and I would consider us to be relatively frugal with our money. Mortgage is small (ish) but certainly still a significant monthly outgoing.
I am just getting a little worried as the state of the ecomony or what is starting to happen and the sector I work in (mortgages) but we'll see, its not quite like 2008 again, but I am starting to see "signs" of it, if I loose my job now thats not going to be fun as last time (2008) it took 4/5 years to get back to where I was, to be honest, given inflation, more like 10 years.