Thanks for raising the issue.
Most probably, people who made that decision are not aware of the implications and made that choice in good faith, so it's worth giving reasons why you want them to avoid proprietary software, rather than just frowning at them.
To the admins of lemmy.world and anyone who feels confuse about why this is an issue : it is about freedom. You all know how Facebook, Twitter, Reddit, etc are turning ugly, and you can't do anything about it. With FOSS (Free and Open Source Software), when it turns ugly, you can do something about it. You (or any technical person who agrees with you) can take the code and go your own way with it (we call that "forking"). No decision of the authors can be forced upon you. Similarly, if you think something is not working right, you can fix it yourself, and send the changes to the maintainers of the code, who usually are happy to get some help. So it's also about freedom of fixing your own problems, instead of waiting and praying the authors do something about it.
And this is the whole spirit of the Fediverse : taking matters in our own hands instead of being betrayed once more by a company which decides that their bottom line requires to be user hostile. One day, this will happen to Discord to, it always ends up there. That's why people using Lemmy who are aware of those problems are not happy with seeing lemmy.world use Discord.
Thanks to the admins of lemmy.world for all the work they provide to the Fediverse.