Tech funding that's reliant on a large number of small donors is less sustainable than a few deep pockets.
However, the latter situation opens the door for somebody to simply become the largest funder and start implicitly dictating its direction, like what Google eventually did with Mozilla.
Surely it doesn't cost $150m/yr to maintain security updates for a browser - is there a cheaper way to fund one? Functionally, it seems that browsers don't do anything more today that they haven't been capable of since 2015. W3C changes occur at a glacial pace too, it's not like there are always new things to be adding into the pipeline.