Yo - the bottom teams not ONLY don't pay their drivers, but require their drivers to ARRIVE with sponsorship of x million that they can give to the team.

So basically, they are paying for their drive.

They also will have earned when they worked in other lower formula's, the teams (the lower ones), just happen to be in a unique position where there is an excess of drivers, so can let the best of the 'rest' fight to get a seat in their car.

You should read up a bit more about how f1 works, as it is fascinating reading.

Cheers,
RW