They don't. Completely the opposite.
www.kudosprime.com
84% of GTS players haven't done a single sport race. Not one. Only 7% have done more than 10 races.
Because we want a GOOD career mode. The tacked on GTS GT League was terrible because it had no progression, no prize cars, and most importantly, it had no actual races. You started every race at the back and passed mobile chicanes masquerading as AI.
Even being awful that mode had better participation than Sport mode with "only" 40% having not done one race compared to the over double for Sport mode.
www.kudosprime.com
Not everyone enjoys online gaming, for one. Secondly, it's what GT was built upon. It's what people know and want. They want to start from nothing, enter races, and gradually build up a car collection.
Like I said, we just want it to be much improved over GTS and past games. Some people probably do just want a copy of GT1-6 but I don't, personally.