goony wrote:...when they earn 10x that amount in private sponsorship anyway
I think you'll find that most of the drivers on the grid can't take any significant sponsorship of their own outside of the team. They're often signed as drivers to bring sponsors on-board but generally what they endorse in ads etc is via the team and that's where the sponsorship money goes. Their own sponsors would be generally be minor ones comparatively.
I recall M Schumacher being a rare case where he negotiated (after many years at the team) being able to wear a German company (a bank?) on his hat in press conferences outside of his Ferrari deal.