Just because cockpit cam isn't like real life, certainly doesn't mean bumper/hood cam is any better. Neither is anything at all like real life. Cockpit with VR is closest by far.
So those choosing bumper (which is definitely too low to be anything like natural to me, on most cars) are probably doing so to be faster, and that's a valid and sensible choice in a racing game. As is chase cam, which I've never used.
Cockpit does indeed hinder speed marginally (I've extensively tested), but that's one reason why I prefer it now; the SP game is so easy to beat (whether it's races at hard difficulty or golding licences/CEs and even most TTs) without some handicap it's all a bit meh... If I were ultra-competitive I might consider switching back to bumper/hood for Sports Mode, but life's too short.
Also, I like to be able to check what I'm driving; back in GT Sport, when I almost exclusively used bumper cam, there'd be times in longer races when I'd forget what I was driving (919 or R18?, X Gr3 or Y Gr3? Impreza or Evo?) and everything becomes just 'a fast car'. In cockpit cam you can look at the wheel or dash to (usually) remind yourself what the car is.
In some of the modern Gr1 prototypes it seems there's more cockpit on view than track, which is just a postbox-style slit across the screen, so those are the ones that present a real challenge to cockpit users, and I like it all the more now because of small extra challenges like that.
And some of the more mental cockpits in the VGTs are not to be missed.