I kept all the gear my sister and I had as teens, which was modest by today’s standards. I’ve appreciated having extra headstalls and bits to play with. We didn’t have turnout blankets, rain sheets, leg protection or multiple saddle pads, the bulky things.
I have had one horse in one barn (for 10 years) since I returned to riding 15 years ago so haven’t had the non fitting gear issue. I have given away a couple of headstalls and saddle pads that I decided really weren’t working. Some years I use all my different turnout weights, other years I don’t.
I think gear gets out of control much faster if you have multiple horses or move around a bit and lose count of what you own.