Mozilla doesn't think the state should meddle in your relationship with them, or the rest of the Internet.
> Why don't they also block every CA residing in the US?
Because there's no evidence they're controlled by the US government in the way Kazakhstan's cert clearly is.
I don't want to have a relationship with Mozilla. I use their browser to communicate with other people. The browser is merely a tool, and I would expect it to allow me to communicate with anyone I want (as long as it's technically feasible), not only people that Mozilla approves of.
Installing a cert in the local root store means 'I fully trust the owner of this certificate'. It is an intentional feature of TLS to use this to be able to consensually MitM a TLS connection.
Yet here, western companies have decided that, regardless of whether the user wants to be Man in the Middle -ed by Kazakhstan, they simply cannot. This is inherently a political and not a technical decision. What Kazakhstan is doing is not actually breaking TLS, but instead using a feature.
That could potentially be fixed with better UI, but even then it's rather hard to communicate the danger when the user is under the influence of a social engineering attack from their own ISP. (E.g. "This certificate is needed to ensure your security. Just ignore that warning from your browser, it's not important.)
Incidentally, the above is why the 'consensual MitM-ing through a root-Cert is a feature of TLS' does not hold op. It is not consensual, it is not even coerced, it is a hard requirement. You could then go into an argument about national sovereignty / complying with local laws, but that is a totally different argument.
Look, I'm as pro-freedom as they come and I'm against coercing people to install certificates, but I also think good tools don't leverage their popularity to push their political opinions, even if I agree with those opinions. Good tools allow their user to do whatever is technically possible, even if the tool maker doesn't like that use-case.
The political and personal relationships of the user fall outside the realm of concern of the tool.
Hardly sounds like a choice.
If my anyone is coercing me to do something, it's a problem between that person and me. I don't want Mozilla lecturing me on politics, I just want to use the browser.
No one's coercing you into using their browser.
I want the browser to let me make my own decisions regarding who I share my encrypted data with.