MapCat
I can't speak for anyone else but in my case it's a combination of things.
The crux I suppose is that I have a well paid job and indulge on something I like.
Having said that, what you have seen has been accumulated over quite a long period of time.
Obviously I change "wet" products like mascara etc regularly, however powder eye shadows/blusher last for ages.
I tend to buy "little and often" so treat myself to a new lipstick for example once a month.
Also a lot of my CT "stash" was the result of birthday and Christmas presents.
I suffer from eczema - which I generally keep under control now - however in my teens it was a nightmare.
As such I suppose I prioritise "skincare" and "make up" in a way those of you with "normal" skin possibly find very indulgent.
That's why there's a trend to certain brands as I know they won't irritate my skin. They are not always high end - astral moisturiser is a staple for me - but drugstore make up just doesn't work for me.
So after trial and error I now stick to Bobbi Brown, Nars, Estée Lauder and more recently Charlotte Tilbury.
For skincare I love Liz Earle, Eve Lom and Astral :-)