Understanding which projects are actively using launchpad is a bit complicated because of the way launchpad is positioned as both upstream project hosting and distribution build system sausage factory. Its deliberately designed to blur the line and make it appear as if project development for thousands and thousands of projects is actually happening there. Just because a project is listed in launchpad doesn't mean its being used outside the context of Ubuntu package building.
For example... Networkmanager has a launchpad project listing...it has bzr trees....it has bugs... and none of it is upstream networkmanager project development. Its _all_ distribution specific packaging work...no different really than Fedora's git and bugzilla that feeds into Fedora packaging. But end of the day NetworkManager upstream development uses the freedesktop and gnome development infrastructure for git and bug reporting. Does NetworkManager as a project use launchpad? Hard to argue that it does. Does Ubuntu as a downstream distributor which leverages the work done in the NetworkManager project make use of launchpad...yes..clearly.
Or take Openstack. Openstack is using launchpad blueprints and bugs but is doing the code development primarily with git facilitated by gerrit using launchpad single-sign-on. I mean holy crap...that's so convoluted...all to avoid using bzr and use git instead. Clearly launchpad does provide some very unique capabilities in the blueprints and bug modules..and that magic that is single sign on. Basically all the not really code management bzr stuff. Is OpenStack using launchpad? Yes..clearly. But not in a way you would expect. As soon as github fired up equivalent services like blueprints and a bug report tool....you think openstack would move to using github's version of those services?
All that is to say that it is quite hard to understand how much "upstream" usage there is of launchpad versus how much strictly Ubuntu integration usage there is in launchpad. Obviously launchpad as infrastructure to grind the sausage that is Ubuntu is quite critical...by design...but that's downstream integration choices...not upstream development choices.
And then there's Canonical's weird approach to for-pay launchpad services..where they have deliberately decided to _hide_ the launchpad item from their storefront. Seriously you can't navigate to the "I want to buy a commercial subscription to launchpad" from their storefront. -EBADBUSINESSEXECUTION
And remember that a lot of Canonical's projects started out as private projects with OEM partners inside the launchpad infrastructure. So the business model aroud the private partnership stuff did make sense at one point...back in the day when HP and Canonical were working hard on Mi (poor Mi) launchpad sort of made sense for private collaboration in that sense but that was a while ago now...before git one the distribute tool war.