Is this a universal truth, or just your experience?I agree it's not really illusionism as per the quantum ogres example, but it is IMO a contrivance; and comes across as a contrivance when done.
For example, if you're fifteen adventures into a campaign and an enchanted glaive has never crossed the PCs' path and then someone brings in a glaive-spec. Fighter, having an enchanted glaive just happen to show up in the next adventure is a bit too contrived, and comes across as such to the players - including the one that benefits.
In my long-running, default-setting 4e D&D campaign, one of the PCs - a Dwarf from the Black Peaks - was proficient in the Black Peak Halberd, a superior version of the halberd that I designed for the player, modelled on the other superior weapons found in the PHB and Adventurer's Vault.
In an early session - maybe the second or third - the PCs confronted a group of opponents from the Iron Ring slavers. One of the opponents also wielded a Black Peak Halberd. The two characters - fighter PC and warrior NPC - faced off in an epic climax. The NPC taunted the PC about his use of the Black Peak Halberd - I as GM took the opportunity to introduce some backstory placing Minotaurs as having played a role in tutoring the Dwarves after they gained their freedom from the Giants. The PC defended the honour of himself and the Dwarves of the Black Peaks, and bested the NPC in combat. And took the +1 Defender Black Peak Halberd as his prize.
No one at the table complained that this was contrived. I'm recalling from many years ago now, but I don't think my memory is doing too much editing in recalling that we all found the scene pretty exciting and worthwhile.