The high-level view of your responses are that they are an attack on the developer of this game, someone who has already put in seven years of effort to get to this point already (as demonstrated in the game development blog). The developer does not need that, and digging in deeper to become more aggressive will not help you get what you want.
There are reasons for not developing on Linux, as there are for other platforms (e.g. MacOS, PS5, Switch). As great as it would be to just drop the same code on different platforms and have it work perfectly every time, that's not the reality. There are *always* platform-specific issues that crop up:
"If you don't design your software with platform-nonspecificity in mind, then it just makes it harder. Nothing is truly impossible to port, disregarding hardware capabilities and computing speed. There's no such comprehensive "tool" for porting games to other platforms, though, since they all work differently under the hood."
https://gamedev.stackexchange.com/questions/49375/what-are-the-main-requirements...
Regardless of your own personal opinions on what should or shouldn't be done, the developer has already answered your question about Linux ports, in particular mentioning that it is appropriate for users to use Wine (in the form of Proton) to play Taiji on Linux. And, if the game not working on Linux is a showstopper for you, the developer recommends you consider purchasing on Steam due to a better refund policy.