IIRC Signal doesn't have a web app for security reasons. With a iOS/Android/Desktop app, you can verify the checksum of the binary against what signal provides.

But with a web app you redownload the application everytime which means you'd have to recheck that checksum every time you use the app. I guess that WhatsApp, Discord, et al have decided that this is a reasonable risk. But the privacy oriented Signal team disagrees.

I don't think it's a prioritization issue, the desktop app is currently running via electron which means it's effectively a web app already.