UPDATE: It seems that all Telltale adventure titles are about to be taken off GOG, too, come 27th of May. We can now safely surmise that this is unlikely to have anything to do with Gearbox, but rather has much to do with the fact that IP rights cannot be restored to a company that's gone down under.
With Telltale gone, what's to say what will happen to all the games that have now been delisted. At the time of writing, you can still purchase certain Telltale games via Steam, such as Guardians of the Galaxy, but it is at this point fair to say that they will likely be gone soon, too. Be sure to grab the games while you can, either on Steam or on GOG!
ORIGINAL STORY: Tales from the Borderlands can no longer be bought on Steam, without so much as a warning. There's been no official word from anyone on what's going to happen with the game now, but the current state of things is that there's no 'purchase' option on its Steam page.
The fact that you can no longer buy Tales from the Borderlands on Steam is both surprising and unsurprising at the same time, given the fate of its developer, Telltale Games, who went under a few months back.
It very well could be that the intellectual property rights are simply being transferred to someone else - likely Gearbox - and that the game will appear purchasable on Steam in some time, though there's simply no way to tell as it stands.
The silver lining is that the game isn't entirely lost to the digital wasteland. Namely, you can still buy a Steam version via Humble Bundle, and the game is also available on GoG, too, so it's not like you can't access the files at all, no matter what, like what was the case with some other games.
Of course, if it's Gearbox who's going to be in control of the game, things are entirely uncertain. They might forego a Steam re-release entirely, and opt to go to Epic Games Store instead, but there's really no way to know at the time of writing. We'll keep you posted as the situation develops.