Think a collection is when you can't find a specific purpose for the bows you have other than to just look at them.
I have eight which is the most I've had at any one time since 1970 when I traded a whole bunch of them off for a fancy takedown target bow and some cool bowhunting stuff. What I have now include several that I call backups, since they are the same model target or same model hunting bows. Another bow was a gift, and one was left from 1970, which was my wife's. The most recent two are low draw weight bows to keep me shooting as time moves on. Those low pounders are becoming some favorites.
Thought hard for several days a month or so back about buying several bows, a '63 Tamerlane and '62 K Mag, which would be exact replacements of my first two bows I ever owned. However, they would have made me a collector, so passed. Got just enough to get by and a few for when I get old.....er.