Money is but one piece to ensure longevity. How many people even work at groups.io? What's their business continuity plans in case the founder or someone critical to the team dies, either due to old age or some sort of tragedy? Or becomes tired of running it?

I'm not convinced it's preferable - people get old and tired of running a thing, or undergo some big life event that changes their priorities, and it's so tiresome to find a successor. Groups.io doesn't have the kind of transparency for me to trust in its longevity. (I am in a group or two hosted there though.)

Meanwhile, large tech can keep something running well past the initial creator's interest as waned. Sergey Brin and Larry Page left Google 20 years after they founded it, but I doubt they've had the same passion for new algorithms to improve Internet search for far longer. Despite that, Google is going to be around for a long time. Can you say that about groups.io? I don't even know who the CEO is or where the company is based.

In the case of google groups, the important thing to realize is that Google is from an older era of the Internet, when people used mailing lists to keep in touch and wrote long form posts rather than pictures on Instagram. So dropping support for mailing lists simply would not work with the current company culture, and something deep ingrained into a company's culture is difficult to change, especially as new employess get steeped into that culture.

I'm not going to deny the idea that Google Groups it's been "left to die", but I'd expect to see a facelift and a upgrade to Google Groups long before it dies, simply because it's an important dogfood product.