It's uncommon for upstream to provide .deb packages. That's not really how it's supposed to work. The Debian community creates Debian packages. Upstream's job is only to avoid making the Debian community's job more difficult than necessary. Unfortunately due to the decisions made by various popular Linux projects (mainly an obscene obsession with dynamic linking), it's not really feasible for upstreams to provide GUI applications on Linux. I hope someday this can change, but realistically there's not enough effort being put towards this goal.
I'm quite surprised they don't provide a .deb package as that checks off 90% of Linux users.