Anyone who thinks that exiled Drow living on the surface is a new thing that WOTC made specifically for 5e clearly hasn't been following the racial migration and progression of Drow from 2e onward.
Drow have been migrating away to the surface for quite a while now, although in the old days their numbers were relatively few, a small number of small communities that lived in secrecy. The Drow underwent a significant racial split in the absence of lolth in the 3rd era, most went to follow the other dark seldarine, but a not insignificant amount took the opportunity to swap over to Eilistraee, whose main things is that she encourages Drow to leave Lolth society behind and migrate to the surface. Eilistraee was later killed by Lolth at the end of the 3rd era for this after she returned from her godly sabbatical. After that, some of the Drow swapped back to Lolth, but at this point Eilistraee had several thousand followers preaching her doctrine, and the loss of a couple hundred was considered to be acceptable.
Eilistraee, Vhaeraun, and all the other Drow gods who got killed off ages ago were revived at the beginning of 5e, lots of Gods were brought back actually, including Myrkul, the shithead. but past events still remain, and the significant population of Drow that were already living on the surface remained where they were.
Does this mean that the "old" Drow have suddenly ceased to be? No, don't be an idiot. I don't understand people who think like this. Your traditional fem-dom Drow still exist, they haven't been erased. There are still more evil Drow than there are good Drow, and prejudice against Drow is still rife amongst many communities, who likely don't care about whether you are a surface Drow or an Underdark Drow. But this gives people another option for playing their characters beyond being a super evil nasty Drow, or being a Drizz't wannabe.
