As much as I'd appreciate more open source for the sake of transparency, binaries provided on websites aren't guaranteed to match the source code provided and I'd assume most users are pulling binaries versus building themselves.

Practically every platform has multiple software stores these days and many FOSS stores make their build logs available. Some take it a step further and provide reproducible builds, which is more or less there as far as source to binary traceability and binary trustworthiness is concerned. These are good enough reasons to open up the source, ignoring the other advantages just this once.

The ability to do so provides some protection. If someone pulls and builds and cannot reproduce the binaries, they can at least try to get the word out. Closed-source prevents even the opportunity. Even source-available is better than closed.