Just like any monopoly, they dominate and then abandon.
They could have funded an independent foundation, or sponsored existing teams, or paid an external agency.
Instead they made a big fanfare, got a lot of attention, and tried to make themselves the arbiter of what should receive attention.
I'm looking at the Wikipedia page for OSS Unicode typefaces and the stuff from before Noto looks to mostly be collections of other OSS typefaces. Maybe MPH 2B Damase had some independent funding? I can't tell. But if these efforts had significant funding it is not apparent from their output.
Based on the information I have available to me at this time, I can only conclude that the space of broad Unicode fonts is in a much better state now with Google's efforts on Noto than it would have been in the counterfactual where they did not make those efforts.
He's been developing the Aboriginal fonts for decades, when many people working on language documentation were only vaguely aware of Unicode. He was very responsive to projects I worked on and added characters into the private use areas whene Unicode hadn't defined characters yet. This allowed school children as well as researchers to use orthographies they wouldn't otherwise be able to use electronically. Many language documentation projects have relied on his work.
The Noto fonts are nice but kind of late comers. Google has a history of making a brief noise about endangered language projects before abandoning them. This site was originally a Google project that was abandoned for years:
http://www.endangeredlanguages.com/
The characterization on the site is that Google always intended to hand it off but the reality is that there was a big noise made by the company and then nothing more than an essentially empty web site sitting there for years until it was taken over by other groups.
Fonts don't go away but I would be very weary of trusting Google with data as important as endangered language documentation. You never know when they'll turn out the lights. They'd do a lot more good by helping to fund and support existing projects that have demonstrated long term commitments.
Android isn't getting updates to Noto fonts - and doesn't support font side-loading. So anyone who wants to communicate using an endangered language can't do so.
Judging by the issues backlog, it appears only a few people at Google work on this. Not enough to sustain it.
This is too important a project to be left to the whims of a Google product manager.