It’s not proprietary, lol. You can download and deploy each of their bridges yourself to your own servers.
Source: been using their WhatsApp, Discord, and Signal bridges for over a year. I use Github sponsors to pay for development, as I appreciate how great they are.
The only closed source part of their stack is their client, which you don’t have to use.
Also, they’re some of the most prolific contributors to Matrix outside of Element. The emoji picker in Element was literally PR’ed by Tulir.
Love it when folk see people trying to make money off OSS and immediately resort to hysterics. It really makes closed source development look appealing if you’re going to be damned by idealogues regardless of whether you release the source or not.