Get old.
Well, I can't say that works all the time. I haven't "stopped" but I've cut way back. At one time I had a safe full of handguns in particular. I honestly didn't know how many I had. Then one day I realized that. "I don't know how many guns I have." I had guns I'd never fired, and had never thought about firing.
So I sold off most of them. I kept a few that I really like and use. Now when I see something I want, I either trade or sell one I've got and get the next one. I've actually reduced the number I kept down a few more. But they're ones I use. At least once in a while.
It helps that now when I look into a display I can say "I've one of those." Also I'm not interesed in anything "new" so I don't care what kind of whiz bang plastic semi-auto just came out.