Possibly off-topic because I don't know how GT Sport's single player fits into this yet, but:
With this trend thats been goin on with racing games lately (all cars and tracks unlocked from the start
IMO an excellent, long overdue trend that means I can jump straight to the content I enjoy most, instead of having to spend time on content I enjoy less, or don't at all. Which, for me, means
more fun.
Now I'm not saying racing games shouldn't have a good sense of progression in their single player modes - the exact opposite in fact. I really wish for racing games to have more ambitious, dynamic and deeper careers than the very familiar "forced to start with a dustbin and work your way through a fixed, mostly linear list of races" affair we're so used to. But I think part of doing that involves giving the player greater choice.
PCARS understands this - it has a progression system, and a set of accolades and goals it sets for you, but you can start wherever you please within that system. It has its own limitations and isn't very well presented, but the fundamentals are there. The F1 games understand this - you have a free choice of team, and your objectives adjust accordingly. Assetto Corsa doesn't fully understand this - it's "career" almost literally is just a linear list of events - but with its custom championships you can do whatever the heck you want, with a bit of setup work (and imagination).
Sports games have understood this for yonks. In FIFA if I want to take some crap Conference team to the Premier League I
can, but I don't
have to. Imagine if you started up franchise mode in Madden and it said "sorry buddy, you gotta start with the Browns.........don't worry, you can unlock your favourite team at level 54 though!". No thanks.
It's probably also worth saying that none of this stuff is a substitute for the
actual racing/driving being fun.......at least, I couldn't imagine myself wanting to play a racing game just for the sake of unlocking things, using whatever arbitrary points/credits system the game happens to have. Likewise, before AC on console got custom championships I still had lots of fun doing single races, because the driving experience was that good. Well, at least with the cars I wanted to drive; I don't know what it's like with the cars I didn't want to drive...........and hopefully I never will!