I'm sure nothing I post will change your mind; I know how internet forums work

. But it's not all that unusual. Look at many of the replies here? And for my table and group, we like finding the unknown treasure and finding out what it is. It gives more mystery to the game, and reinforces the living world concept we all prefer. If we knew we'd get magic items we all wanted, it would make the game feel just like an exercise in optimization, and we don't like that.
So we're either all lying here, or we do in fact don't customize
It's not binary, and pretending it is, is well, a terribly naughty straw man.
The reality is, I would suggest, that almost all DMs customize treasure, including magic items, for their group. But how much they do it varies wildly. It's this false claim of "purity" I object to. Claims of purity are not only almost never true, they're toxic to honest discussion.
Your post here is a good example of that kind of toxicity (though I accept this is likely accidental and not malicious on your part). You present a totally false binary. You say either it's all totally random, or "we get all the magic items we all want". Neither is the truth. DMs who customize what they give out obviously do not give players "all the magic items they want", do they? Come on. You know that. I know that. We all know that. DMs who rarely "customize" loot, do, in fact, re-roll hoards they think are too generous, or too boring, or inappropriate to any number of things - including the group. I know because I've been at both ends of this spectrum, and I've seen many other DMs who were all over the spectrum, in the last thirty years.
What you also seem to be doing is conflating two different things:
1) Wish lists.
2) Customizing loot.
You seem to think these are the same thing? You talk about "unknown loot", and like that's the only explanation I can see for you saying that - you think these two things are the same thing. They aren't.
Wish lists are a 3.XE/4E phenomenon from when the game hard-expected a certain amount of magic items at a certain level (in 4E it was easy to remove this expectation - they even had optional rules for it - in 3.XE you just had to work around it, and it didn't work well because all the numbers expected certain items at certain levels, particularly the infamous Cloak of Resistance). They lead to customizing loot, but customizing loot does not lead to them. I customize loot, these days, to ensure the PCs get items I know funny naughty word is going to happen with, or that's going to be really cool, or that's going to cause some sort of amazing crisis or the like (or a narrowly-dodged crisis, which players love). That doesn't mean a player goes "Gee golly Ruin, I sure as heck wish I had a Holy Avenger +5!" and lo and behold, a few sessions later, what should they find! It means I look at the group, and the players, and the characters, and whilst I randomly roll a lot of the loot, I might replace an item here, or add an item there, to make it more fun for everyone involved.
But you're equating this directly with giving people exactly every item they want, and that is simply not how it has ever worked.