I feel like that's a problem with too many of them being focused on a few specific Pokemon that barely get used (the plates and drives alone are 21 items that apply only to Pokemon that most players will never even encounter), the items themselves not being that useful even then, and the fact they keep making them one-of-a-kind things that you get dumped on you when you don't want or need them. (Admittedly, the last point applies to these box legends aswell.)
The actual number of Pokemon that benefit from those items is fairly small, if I recall correctly. There's Farfetch'd, the Latis, Marowak, Chansey, Ditto, the creation trio, Pikachu, Genesect, Silvally and Arceus. I think that's it. Very few of those are actually useful even in metas where the Pokemon is allowed. The rest are all Mega Stones (themselves a significant source of that bloat, especially in SM if you were claiming the events), Z-Crystals or key items pertaining to random legendaries.