What's hot now, by the time you have worked your script to fit it, done the door-knocking (usually with your head), got the script optioned, the thing goes into development... and the various rewrites have happened. It ain't hot anymore. And the development execs got fired and all their projects got dumped, except the one that had Tom Hanks attached and they took that to their new job at the new studio.
As has been said, just write what you love.
'Cos ultimately, in truth, odds are (if you're lucky) what you write will be a sample that gets you hired to rewrite something someone else did, but during rewrites it got cool. And the development execs who was working it got fired and all their projects got dumped, except the one that had Tom Hanks attached and they took that to their new job at the new studio. And what you suddenly have to work on was one of the dumped projects that someone found after enough time had passed and convinced a studio exec that if they could get this reworked and Tom Hanks on board, this would be a shoo-in.