Because they lack even a modicum of creativity and they know that their pastiche self-insert social agenda megaphone characters go over about as well as a turd in the punch bowl at a high school dance (see: the New Warriors reboot that didn't get off the ground). They need a way in to be able to blast their message to as many eyes as they can and they can't wait for their trash to gain popularity, so they co-opt existing characters into their agenda (Iceman, Tim Drake's Robin, Squirrel Girl) or replace them with race-lifted Mary Sue versions that are supposedly better than the originals (Riri as Ironheart, Sam Alexander as Nova, Kamala as Ms. Marvel, Amadeus Cho as Hulk, et cetera).
Because they lack even a modicum of creativity and they know that their pastiche self-insert social agenda megaphone characters go over about as well as a turd in the punch bowl at a high school dance (see: the New Warriors reboot that didn't get off the ground). They need a way in to be able to blast their message to as many eyes as they can and they can't wait for their trash to gain popularity, so they co-opt existing characters into their agenda (Iceman, Tim Drake's Robin, Squirrel Girl) or replace them with race-lifted Mary Sue versions that are supposedly better than the originals (Riri as Ironheart, Sam Alexander as Nova, Kamala as Ms. Marvel, Amadeus Cho as Hulk, et cetera).