Because I can is the best answer any of can give.
For myself, its a cost per shot thing. I cast lead I get free. So, my reloads cost me what I spend on 22LR that my kids shoot till its gone.
Man, its not about stopping power, penetration, or stopping a "BG".
45ACP is all about the feel. The feel of a finely tuned 1911 slide doing its thing. Slamming closed on a fresh round. The push rather than snap as a spent case is ejected and a fresh one is stuffed in the pipe.
The 45 thing is hard to understand till ya really start shooting one. A lot.
No disrespect intended toward any other cartridge, but "that's the way it is"
This is just my humble opinion.