Hear hear!
For some it's the offline races, for others multiplayer.
If GT had the same FUN online experience FM has been having for the past 12-14 years or so (lots of different car classes, easy matchmaking with full 12-16 player lobbies, constant track rotation, tuning setups allowed, microphones, vote to kick players, events to earn unicorn cars etc) and a decent rewarding economy system, I'd be playing GT7 non-stop and earning credits, instead of constantly checking forums and doing other things in my free time.
(I would still be playing FM7 instead of GT7, if my XB One didn't break.)
From the little online racing I have played using a friend's xbox and what I have seen online I think FM has a horrible online experience (talling about the racing itself), sport mode has its issues but it is by far my most enjoyable experience racing online on consoles.
Fully agree the single player needs more content however, plenty of legendary cars have no events to be raced on which is a massive missed opportunity and makes buying that £20 m legendary car you love a bit of an anti climax.