I have been in this hobby for quite a while. The answer for me is diversity.
I have
2 newer Sterns
4 Williams dmd games 90s
4 classic early 80s Balls
3 classic early 80s Sterns
2 system 11 games.
I often find I go through spells with each generation. Depending when you asked me over the years I could have sold all my dmds for balls from the 80s or vice versa. However I'm glad for variety. Mix it up a little.