I think it is more along the lines of just having filler cards in packs that will superficially look like something cool to a kid who is only really interested in collecting current players they like. Most adults understand that these types of cards arent anything special, except there probably is some confusion, probably intended by manufacturer, by putting these cards as serial numbered, "relic", and/or signed. If there is a relic of retired player, I think its nonsense to think it was actually game worn or that it has any significance other than just being a card with some fabric on it (its a piece of an authentic replica?). In theory, it could be of a historically signficant game but then its hard to believe the player or anyone would have kept whatever it is (jersey, bat, etc.) and then decided to effectively destroy it by cutting it up into little pieces -- it would be more valuable to keep it intact (either monetarily if the player really wanted to get money from it, or sentimentally to player or whoever ended up with it). I would have a really hard time thinking that a player would have just kept some random jersey or ball from a game unless it could be tied to some unique game (last game, first game, world series) and in that event the card should be able to specify that.
Signatures on cards of retired players probably can straddle the line of being something of value to a collector, but I personally think of this as the equivalent of just having a player's signature on a napkin or anything else as opposed to a collectible trading card (and if player is still alive, who knows how many signatures have been signed and will be signed by that player). The only big exceptions would be ones in the early 90s of Reggie Jackson, Ted Williams, Mickey, etc. given they were the first ones of their kind and no signed cards during their playing days.
I think it would be fun to try and put together a proclamation of what is or is not a legitmate collectible sports trading card and see how complicated it would get to try and fit in all the types of cards people have some interest in, like "the card shall be of a player actively engaged in a sport and has yet to retire from playing the sport, or who retired but subsequently unretired, except cards of retired players shall be permissible in current sports-related positions provided that it is of a set, subset, or insert set that includes all other individuals in the same or similar sports-related positions irrespective of whether the individuals played professionally. This includes, but is not limited to, sets of current sports announcers with announcers who never played the sport they cover, professionally or otherwise."