Because they KNOW their mush won't sell. No one wants to watch "Suhlkrah Arhmanara and the mystery of why I hate white men". But you say "hey wanna watch an AU of Scooby Doo? Itll be super funny" and you get a few thousand people in a seat. Same reason why Rattatoing exists except at least that movie had the decency to not insult Rattatouli fans.
"Scooby-Doo will not feature Scooby-Doo"
...Then why is it Scooby Doo? Make a film about some brown front-hole-haver and its friends. That's clearly what they want to do, after all.
Because they KNOW their mush won't sell. No one wants to watch "Suhlkrah Arhmanara and the mystery of why I hate white men". But you say "hey wanna watch an AU of Scooby Doo? Itll be super funny" and you get a few thousand people in a seat. Same reason why Rattatoing exists except at least that movie had the decency to not insult Rattatouli fans.