There are approximately 50 available trans actresses worldwide and as far as I can tell, MAYBE a handful of actors.
If I were casting a film and needed a trans actress today, filtering for age, nationality, ethnicity, talent and screen presence- depending on the part, I would probably find myself with two, one or even zero candidates from central casting. Let's face it, the pool isn't exactly overflowing with transgender talent. I should ask my producer friends how many they can find with SAG/AFTRA cards.
Producers in Hollywood don't like taking big risks, and limiting yourself to only a couple of possible choices is a huge risk, as is auditioning an unknown party. It's still much easier to find a cisgender actor with serious chops than it is to teach a transperson to act.
If we want to buck the trend of having lead trans roles being portrayed by cis actors, we all need to work on our acting, and fast.