At least anecdotally, I'm not sure I can find a whole lot of supporting evidence for this -- the vast majority of the commercial applications I use on a daily basis let you install them on any compatible system that you own. This isn't just a byproduct of "well, they're not checking"; it's usually explicitly written in the license, it happens with programs that make you enter license codes they validate before running, and notably, it's very explicitly the model of the Mac App Store. Sometimes the license says only one copy of the program can be in use at a time without a site license, but for individual use that's generally fine in practice. (I haven't seen a program that's actually annoying enough to check for running copies of itself on a LAN and shut down if you're violating the license in decades at this point, although I'm sure they're still lurking out there in weird niches. It sounds like something Autodesk software would do.)
Anyway -- maybe running programs remotely using the Xserver model never took off in the Mac world, even after OS X, because there was no prohibition against just installing the software on multiple machines? In practice, it's not something I've missed very often, I admit; while I sometimes like to edit text files remotely, that's not something that feels like it would really be improved by this model over using a local editor that can open files over the network. (Edited to note that I'm not suggesting there aren't still valid use cases for X11's server/client model! They're just not ones that have impacted me; if they did, I'd run XQuartz, which I don't love, but it'd probably get the job done.)