It was mentioned in
the thread on this, drivers had a one-time seasonal atrophy applied after launch.
The way levels work has changed fundamentally. When you level up now you don't need to train your driver up again or buy new ones, they will remain 5 stars even through level transitions. This is especially useful at lower levels, where levels cycle very quickly. In iGP Manager 26 100% skill is retained through level upgrades, but what happens instead is at the end of each season a 10% off-season atrophy is applied, so that training resumes in the next season.
This also has the effect of addressing max-level being completely static with nothing to do.