I don't disagree and I definitely trust a Finnish company founded by former Nokia engineers a lot more than Google or Apple. But I think there is a lot of overlap between both the "buy European" movement and Fediverse users and those who prefer open solutions wherever possible. A lot of those people would prefer a solution where the userland and/or kernel and/or SDK is completely open source. They will have to weigh their options based on the fact that while SailfishOS is more open than Android or iOS, it is not fully open source.

By the way, it is also worth noting that unlike Google, so far Jolla has been moving in the direction of open sourcing more components of their OS. No one can predict the future, though, and some people would prefer to avoid any possible future vendor lock-in.

Well even though I do think there's value in that despite Sailfish being partially closed it's still a valid criticism.

That's a very glass half full way of looking at it but doesn't that apply just as much to Android?

Nemo Mobile aims to do exactly that.