Sub-Zero and Reptile have completely different voices though and his Baraka voice is the exact same as his Reptile one lol
Imagine Baraka versus Reptile and it's the exact same voice, same dialect and all, just with deeper autotune. That's already two characters he's going to have to do all that voice work for. It's not like Troy Baker who did Fujin, Shinnok, and Erron Black. Or Kelly Hu who voiced D'Vorah, Sindel, and Frost. Fujin, Sindel, and Frost all had very limited lines in the story. (They were probably only asked to do them because they were already on the lot to do the playable characters who have a lot more lines.)
So, Steve Blum's already playing Baraka and Sub-Zero, both of which have all that dialogue. I'm guessing that even if we do see Reptile, he'll be a story mode NPC. But even then. There's only so many reptilian scratchy throat gurgles that one man can do to differentiate a character from another.
It's possible they could get a new voice actor entirely for Reptile though.