Why can't I change my resolution

Why doesn't such a great game have to ability to change the screen resolution? Is there something that I am missing?

The game runs at whatever the desktop native resolution is (it's down to how the UI is built- the entire UI is essentially a web browser for easy cross compatibility with Windows, Mac and Linux).

There is an option for "resolution scaling" which allows you to change the resolution of the main 3D part of the game itself. If your having performance issues the best option is reduce the resolution scaling option to less than 100%.

There is also a mod available to allow you to scale the UI up or down if that is the problem.

BTW, I have a strange feeling that game is forced to run in fullscreen borderless window.
Can anyone confirm this is true?

Awkwardness with the UI mostly.
I can already tell that Totalbiscuit is going to slit his wrists over this once he makes a WTF is on PA.
It'd be cool if there was the possibility to resize the UI like you do with a regular browser window. Not sure if that'd be an easy implement, though.

It's likely not just easy, but super easy. Main problem it's fact UI changed all the time and such mod need to be updated together with game.

It's correct. Rendering resolution might be adjusted with "resolution scaling", but UI is always stick to monitor resolution.