Likely the idea is to let upstream to package once and ship it on all supported platforms. This way there is no constant support/packaging required from distro itself.
As to why snap format specifically, that’s probably allows them to make changes as needed without asking anyone.
Further, if you are tunnel-vision focused on profit, remember that if you lose your end users, you lose your only means to eventual income.
There is now a very nice summary comment from worik elsewhere in the thread, but basically end-users are no longer the same from Canonical’s perspective and so it’s probably wise to thank them for good things they did and move on.
As to Canonical, the only reason I use FF anyways is because it is the lesser evil. They are far from stellar with their constant attempts to inject invasive monetizers into the browser.