Seegee:
Largely because Daredevil and Black Widow occupy separate parts of the MCU. Daredevil was in the Netflix series and Black Widow is part of the bigger MCU films.
Major mistake there from the studios. I think Daredevil and Black Widow shared the same comic book for a decade as a team. But I guess it comes down to who owns the rights these days, like the heavily decimated and often split X-men team. I'm devastated though that no other superhero stepped up and filled in when legal issues prevented Daredevil from fulfilling his historical duty. I can imagine the next panel though, Daredevil in a cast, through broken teeth mumbling, "it was worth it".