Publishing guitar tabs is a copyright violation, but not in the same sense that pirating a CD is. Copyright encompasses several rights, including the master use right (rights to the recording itself) and the print rights, which are what’s at stake with guitar tabs.
Many sites, including the late, great OLGA (On Line Guitar Archive) tried to claim Fair Use as a work of scholarship/education, but were rebuffed by the courts. It is legal to use works under those conditions, but not so much to run a for-profit business predicated upon that.
I’ve used Ultimate Guitar Tabs for many years, and they are very much a profit site. There is some sort of license funny business going on, because they have a very deep archive of often exact transcriptions (along with piles of half-assed approximations), yet don’t seem to get into copyright trouble. This is also where most of the old OLGA content seems to have been rolled in to.
Other sites I’ve tried to use for awhile, such as https://www.jellynote.com/en/, are frustratingly constantly getting stripped of content from takedown notices.
Ah, thanks, that explains it! That seems a pretty sweet exclusivity deal, no wonder that other interesting competitors and services keep getting squashed, and why UG’s database and media capabilities seem stuck in 1995.