Then look no further than public institutions, where (leaving everything else aside) almost every tender is public [0]. You'll never see Thunderbird in any of the submitted bids because there's no company behind it to write the bid and put its weight behind it.

It's a good canary to see if a service or product has anyone capable of supporting it, or if it can be monetized in any way. This doesn't have to be the developer, just any company that can realistically push it into the corporate world.

[0] https://ted.europa.eu/TED/main/HomePage.do