Because of Star Wars doing it like that first
Eh, Trek shouldn't really be copying Wars for stuff like that. It looks annoying (to say the least).
There's a reason why I call them "Ultra Dense" Asteroid Fields instead of standard Asteroid Fields.
You do realise that if you had 'ultra dense' asteroid fields like Trek frequently portrays them, they wouldn't really last at all but would in fact attract each other due to gravity until they form something akin to a rocky planet.
In short, that kind of asteroid field would't be sustainable by a long shot.
In the shows, nothing was stated that those asteroid fields were 'recently formed'... as such they really make little logical sense.
That's not what is being portrayed.
Maybe it should be.
I'd like to see Trek using established in-universe figures for example to portray them in VFX for a change. Would cause a 'blending' of real and science fiction.