Chromium was due to the absolute nightmarish amount of manpower on Canonical’s part it took to keep up packaging with releases. Copying Debian’s work wouldn’t have helped because they had and still have fewer resources than Canonical did to commit to packaging it.

LXD ships a private version of a library as it has changes not accepted by upstream. It pretty much needs to be a snap as it doesn’t fit into the realm of .deb packaging due to that.

Two fits “some”. Off the top of my head I cannot recall anything else that has a .deb that diverts to snap. More might come in the future perhaps. 2020 has not been the kindest of years to bookmakers in Vegas and elsewhere.