What bothers me most about such decisions is that I am denied access to the official discussions (and sometimes even the tech support) of the product I paid for, unless I'm willing to maintain yet another online account and accept the third-party platform's terms of service. And those terms are always invasive, designed for that third party to get away with collecting as much information about me as possible.
Discord is another common one. It's a sure-fire way to lose me as a customer.
If businesses don't want to host their own community-facing tools, they should put them on an open platform that respects users' privacy.