It matters cause those actors are choosing to appear cis for one reason or another. Being closeted doesn't make you any less Trans then an out Trans Person.What if they are? And more still, what does this hypothetical actor or actress matter to the trend being discussed? There already are transgender actors who want to play these characters.
They shouldn't be forced out of the closet for a Trans role just because another actor is more open about it.
Would Stealth Trans never be allowed to play trans roles?
This is just one the big problem with saying Cis Folk shouldn't play Trans Characters. It activity removes large parts of our own community because they do not act a certain way and they want to be a woman and not a trans woman or have anything to do with the label.