Which is why I think Obsidian is such a weird piece of software. It's free. It doesn't lock your own data behind a paywall. But, it only allows you to modify it in very specific plugin API ways. I pay for software all the time, and I don't expect it to be open source. But for software I don't pay for, I do expect it to be open source.
That is an interesting point, and you are probably not alone in that opinion. From a logical point of view, it makes no sense to me, though. Just view it as a purchase that costs $X, but where the author of the software provided you with a voucher worth $X. Why should not paying anything for the software give you the right to modify and fork it as you like, whereas you accept that constraint for software you paid for? Just accept that there is free software which is not open-source. You don't have to "buy" it.
I think my thought process goes: I prefer free software (as in freedom, not beer). But, sometimes the author wants to charge money for it so they restrict that freedom to protect their business. I have yet not fully grasped the author doesn't want to charge money for the software but they restrict that freedom anyway.
On the other hand, that may be part of the reason why Obsidian has such a rich plugin ecosystem. Perhaps there is less of an incentive to build a good plugin API if you can just tell people to fork instead.
That's fair. And vim and Emacs have been forked in the past, so you may be on to something there. But, I still expect my editor to be open source. I might be weird like that though.