Because your "privacy focused nonprofit" is itself funded by those very same "multi-billion ad companies".

Sure, so this means they are now a multi-billion dollar advertising company as well?

If a tobacco company makes a donation to a cancer research charity, do we now hate the charity?

The money flow itself doesn't invalidate them. They have multiple bidders for their defaults, and that isolates them from the whims of their funders. The funders are just customers.