We have all been there at some point. Reason number 1 is you are likely full S rank for driving standards, often this results in low DR A drivers being placed with high A and A+ drivers. Then, you may be quite fast in qualifying, bit of a demon, so the game is pitting you against really tough opponents.
I'd suggest hitting a few walls and drop your SR to a low S, this will help but there will be more chaos in races.
I am a fringe A/High B driver and with a full S bar, I can get placed with High A drivers, I simply cannot keep up.