When I was a kid, the limiter was the allowance I had in my pocket, plus the lack of information about what was out there (pre-internet/smartphone days). But then, things seemed to move slower back then anyway, so it all balanced out. I built what I bought on the same day. I never had a storage problem, because every New Year's Eve I'd go to my friend's house and we'd blow up all our broken models.
As I got older, like many others, I started buying better and more expensive kits. I still blew up the old ones up until high school, but by college I stopped. I began to appreciate finished models more, and once I started a full time job, I realized I could afford pretty much anything I wanted. This was the start of the Stash. I pretty much much bought anything that caught my fancy whenever I saw it, and so the Stash grew.
Contests and trips to Japan were another source of model purchases, especially the trips to Japan, where Tamiya and Hasegawa kits were 1/2 price compared to the US retail. I would go nuts and buy as much as I could fit into my suitcases. But as time went on and the Stash grew, it became obvious that there was a limit to what I could hoard. The last time I went on a trip was the 2018 IPMS Nationals, and I brought home only two kits, one of which was for a friend.
I still buy whatever I want, but temper the "buy this" finger by asking myself if I have room for the kit. There are certain things that break straight through this feeble resistance, like Airfix's upcoming 1/72 Avro Vulcan B.2.
The real deterrent for me now is the fact that I have witnessed several modeling buddies passing, and they all left behind enormous numbers of kits (which dwarfed my own but that's besides the point). Helping their families try to sell off the kits has been arduous to say the least. My sister told me that if I did that - she'd kill me. I don't know how she'd do it, but I believe she would find a way to deal me a second death!