Hi, trans actress, writer, and director here.
While it would have been interesring to see Johannson's take on this part, as she is a fine actress, it comes down to who we are.
Trans people, almost by definition, are held to a nearly impossible standard. As a trans woman, I can't be too feminine or I'm just a fag. Nor can I be too masculine, or I'm a potential sex offender. It's a running theme that every trans person, actor or otherwise,are given the third degree by nearly everyone they encounter. Imagine meeting a stranger who only decides to treat you with respect or with cruelty, depending upon what's between your legs. Trust me, its no picnic.
From an actor's perspective, this is also a death knell. These trans actors go through the same schools, can say the same lines, and are just as valid as their cis gendered counterparts. However, nobody wants to cast trans people as anythinf other than an afterthought, for rhe same "whats in your pants"bullshit i mentioned before.
For an actor, a role is LIFE. That means they can pay their rent, buy groceries, you know, live like an actual PERSON. And if people like Johannson are soaking up roles that a trans person can play, then thats how many actors out of work.
Take the example of Zoe Saldana, who is effectively playing every prominent black woman you see. There are plenty of black actresses who are up and coming, and need a break. If Saldana hogs all the good parts, how is anyone going to know about anyone else?
Of all people, Dirty Harry said it best: "how the hell is someone supposed to get experience if nobody gives them a chance?"
RE: Name one famous transgender actor!