Http is just clearly not made for the current state of the internet. It was obviously made for much simpler uses cases but has organically grown together with the internet. This has led to numerous hacks and workaroudns which often became the defacto standard to do things on the web. It's not necessarily an easy problem to solve, client server communication is hard. But http protocol seems like the least effective way to do it, but almost impossible to replace now.
I was recently trying to link our source code against a newer version of LLVM that had introduced a few API changes that I couldn't make heads or tails of. Without the git log I would've had to manually compare the changes and figure out what they meant, or just guess. But luckily the commit messages quite clearly explained what changed in most cases.
Obfuscators, I work for a company that builds mobile obfuscation at a compiler level (LLVM ir and Java bytecode). There are also gaming companies that use similar techniques and technology for anti cheat engines.
I also often see job postings for compiler developers in the embedded field.
Why would you store all of this valuable information in a proprietary tool? What happens when notion shuts down, jacks up prices, makes feature changes you don't like, etc etc? Make some attempt to migrate all this data? It's gonna be hard to do this in an automated way, if they even have an (export) api for this.
I'm using (vim)wiki/gollum and I feel much safer about my data.