I can understand why people do it. It doesn't bother me at all.
People will copy and if you're in the arena it's a problem.
I've seen some people using copying avatars to troll people, they'll be drama between 2 people and one of them will make a separate account/mule with a nearly identical name (I'm not sure if you can have similar names now, you used to be able to) and avatar to troll the other person (and if the names are close enough on quick glance) they'll even try to trick the other persons friends.
I used to hide mine a long time ago because I used to be active in the CB and people would look at your equip list, if they see a few expensive items, they'll spam your PMs with scams, begging or worst case try to hack you. (some people might leave it hidden, as a hold over from the old days?)
If I really want to know an item I just screencap it and post in Q&A or AT.
AT know all the items and you'll literally have the answer in a matter of minutes (sometimes less than that, every time I've posted an item question in there I've had the right answer in no time at all).
To be honest I don't think it's really any different from seeing something cool in someone's sig but I don't know what it is. I'm not going to throw a hissy fit (not aimed at OP) because there's no button that automatically tells me. I'll ask them or someone else or try to google it...
As for catching up on items...I've never really taken a hiatus from Gaia so I don't know the answer to that. but Ridley's
Master Lists would probably be my first port of call.