IMHO it isn't. We just have a lot more patterns, handle materials, etc. to chose from than the "modern" crowd.

They are limited to brand, steels, locking mechanism... and maybe a couple other things.
I'm not a "collector"; An "accumulator" would be a more apt description, I suppose.
I don't limit myself to one or two patterns, handle materials, or any specific brand(s). That would be "boring" … at least for/to me, and no doubt I'd miss out on a good user.
(although there are brands I will never buy for budgetary reasons, and I won't buy a Frost. based on the ones I had as a kid. I even know where all those Frost "knife shaped objects" I had are, too! They be in the mud on the bottom of the Mississippi River, near center stream, as far as I could throw them, north of the vicinity of the (now gone and replaced) old US Highway 136 bridge.)(If they had been merely placed in the trash, someone might have "rescued" them from the land fill.)
There are "too many" patterns I like (more than I don't care for at any rate.)and a several I've yet to try.
As for slipjoints, generally speaking, I don't go for the single blade models.
The multi-blades (with different blade profiles) are just so much more versatile. (One reason I never really "got onto" or have any moderns. I also detest pocket clips, don't need one hand opening (yet) ...), or EDC a fixed blade/sheath/belt/neck knife.
Off hand, the only knives I can think of off-hand that I might get for a "user collection" would be the Rough Rider "Riders of the Silver Screen" series Moose pattern knives. There are just five in the series, and I am "only" four short of a "complete set". I suppose I should get the other four while they are available and affordable.
(not sure about the Zorro knife though. I never understood Mr. Zorro, nor why the bad guys didn't just shoot him and be done with it/him before he got close enough to use his whip (I think he had a whip) or carve his initial on their chest.) If I get a Zorro, it will only be to complete the set. His will not be carried or used.
No doubt Rough Rider will drop them eventually or soon, and prices for those in-stock at dealers will double or worse.