I mean I guess the original thought was Mordo to be the villain in the sequel since the end of the first movie teased him of being the next villain

However I guess both Scott Derrickson and Sam Raimi wanted a different villain that being Scarlet Witch

They never said he would be the villain of that movie. Just a villain for a future movie. A Doctor Strange sequel was only the most likely, but not guaranteed. And of course, plans change.

Of course, there’s always another movie to do that.

One of the earlier scripts had Mordo-199999 being decapitated unceremoniously by Wanda lol, so be glad he's actually still around for a future project.

Well, i guess. Buut did she really have to commit sucide i wanted her in the avengers 5 team