Why?
Because Google is a major source of funding for Mozilla. I don't remember details, but they tried to be funded by other search providers. It didn't provide enough funding, though.
I guess promoting Google search is essential for them to keep building great products. And guard net neutrality. If we don't like it, we are probably not donating enough.
I buy their VPN but can’t use it due to lack of Mac support. Nice way to support them and show them they can build useful services we will pay for simultaneously.
Shameless plug!
You can use MozWire[0] to generate wireguard configuration files for Mozilla VPN.