The only thing good about F1 is the pre-race hot chicks

j/k.
As for Nascar, LFS could probably never duplicate that series correctly due to all of different rules and such that this game does not have. I love Nascar but I didn't purchase this game for that. I purchased it for the sheer enjoyment of racing period. Plus without real-world tracks, Nascar, Indy or Champ cars just wouldn't be the same.
IMO it takes just as much $$ and engineering a chassis for ovals as it does for road racing. Sometimes more in some cases.
So after all that I would say what's the big deal? If someone wants to build models for these different series, go ahead. If you don't want them, don't install them. Personally I probably would d/l just to have them.
But I will say this if LFS dev's did delve into stock cars, it would be HUGE because the netcode is superior to most games out there.