Every campaign is different. Because of that, it can be hard to write books of magic items or similar subjects. Sometimes you need something a little more specialized.
What if in this campaign (or story arc), the party is against a whole bunch of werewolves or were-whatevers. Now you need a list of magic items that are nearly useless in any other style of scenario. You’ll want enchantments that make it easier to turn, force a turn, special silver delivery missiles, protection spells, protection from silver spells, more powerful beast forms (spell? ability?) and what the value of a werewolf hide is, or maybe just the fangs. Do they retain their fur if killed as wolf or do they revert back and therefore there is no pelt?
The point is not to dwell on a lycanthrope based campaign, but instead to show that there simply are times that where the game master will want to put a little more effort into coming up with things that are not in any of the rule books. Honestly, Dragon Magazine use to be good for that. Truth be told, 30 years ago if you were reading the magazine, you either went, “That’s so cool! I’m using that!” or you said, “That’s so lame, why did they waste ten pages on something no one would ever use.” Chances are, different people said both those things about the same articles.
I like specialized campaigns, or at least the story arcs. Spend four missions going against a similar enemy, then take two or three off and then go back to the main theme. It really holds the campaign together! Making up magic items is so much easier than you think, and if you don’t want to make them up, just give the bad guys special powers. “Anytime Bart wants, he can summon a flock of seagulls.” No, not the music group. You don’t always have to put a die roll on it, just let him do whatever when it is cool.
Too many “traditional” campaigns have no continuity. They are just a series of missions performed by the same characters for no real reason, other than possibly because someone would pay. Fighting various types of weres, or undead, or dragons, or slavers, etc - players remember that. They remember how they had to work their way through the lesser critters to find the big boss at the end of four missions. They had to earn the fight. They’re also a lot more excited by getting some minor magic items that specifically relate to their immediate danger.