The great thing about adaptations is that you get to change and reinvent things, so you're not hampered by the limitations of the source. So if you can take an obscure character and find a way to reinvent them and make them more interesting, that's great. Heck, the problem with the bigger characters is that so much has been done with them already, so much baggage accumulated. There's often more room to be creative with the less well-known characters.
Is it strange to me that animated adaptations are drawing on more obscure characters? At this point, not at all. There have been animated shows based on DC and Marvel pretty regularly for the past 20 years now. Naturally the makers of the newer shows want to do something fresh and not just repeat what their predecessors did.
As mentioned before, B:TAS was the screen debut of many major and minor comics characters -- Harvey Bullock, Leslie Thompkins, Mayor Hill, Two-Face, Poison Ivy, Ra's al Ghul, Talia, Killer Croc, Hugo Strange, Rupert Thorne, Bane, the Ventriloquist/Scarface, Man-Bat, even obscure folks like Professor Milo and the Crime Doctor. Its contemporary X-Men and Spider-Man shows were also the screen debut of a goodly number of Marvel characters, including Rogue, Beast, Gambit, Jubilee, Bishop, Moira, Mystique, Sabretooth, Apocalypse, Mr. Sinister, and dozens of others for X-Men and Mary Jane Watson*, Anna Watson, Harry Osborn*, Debra Whitman, Alistair Smythe, Morbius, Hobgoblin, Venom, Shocker, Silver Sable, Madame Web, the Beyonder, Silvermane, and many others for Spider-Man -- indeed, Nick Fury made his screen debut on that show!
*(A character called "Mary Jane" and loosely based on her appeared in a 1970 Spidey cartoon, but she was barely recognizable as MJ Watson. And Harry appeared in a 1992 demo film that was never aired.)
And pretty much every DC or Marvel show that's followed has introduced characters that weren't seen in the previous shows, or gave bigger roles to characters who were barely used in the previous shows. The Batman debuted Black Mask, Rag Doll, and Gearhead. The Brave and the Bold debuted dozens of characters from Jaime Reyes/Blue Beetle to Ambush Bug. And so on.
So far from being a recent trend, this is pretty much the way it's been done for a generation. Strange? Not even slightly.