Often? Only in case of Upstart and LXD (I'm not familiar with the latter's history).
Here's Mark Shuttleworth in 2010:
The next major transition for Unity will be to deliver it on Wayland, the OpenGL-based display management system.
We came to the conclusion that any such effort would only create a hard split in the world which wasn’t worth the cost of having done it. There are issues with Wayland, but they seem to be solvable, we’d rather be part of solving them than chasing a better alternative. So Wayland it is.
https://www.markshuttleworth.com/archives/551
Then in 2013, Unity 8 was released with Mir.
Snap was largely developed in parallel with FlatPak (called xdg-app initially).
There was a talk about the plans at GUADEC 2013:
https://www.superlectures.com/guadec2013/sandboxed-applicati...