You're correct, but I guess they're banking on their users preferring to get the binaries straight from the source instead of through an unaffiliated third party. There are also other benefits to paying, such as being able to file issues against the official repository. Seems like a pretty reasonable compromise to me, to be honest.

The license even says you may redistribute the binary you acquire from them:

> User may redistribute the Binary Release received under this Agreement, provided such redistribution complies with the OSI License (e.g., including copyright and permission notices).

https://github.com/wixtoolset/wix/blob/main/OSMFEULA.txt

> I guess they're banking on their users preferring to get the binaries straight from the source instead of through an unaffiliated third party.

Yep. It turns out a lot of companies are willing to pay for maintenance but they aren't willing to pay for charity. The EULA is what activates the internal corporate mechanisms to make that happen.