This makes new bill more responsive to the specific budget problems each agency is facing due to COVID. Many regions underfunded in the CARES Act (like New York and Seattle) are now in line to receive proportionally more from this package. Others received aid greater than 75% of their operating costs in the CARES Act, so they would not get additional funds through this bill. Many fall in between, with grants that bring them up to the 75% cap.
Yonah Freemark has more estimates on Twitter:
The bulk of the funds will presumably go to Metro and Sound Transit.