My best guess is a combination of historical inertia and the fact that the names are actually meaningful, just not in the way that one might naively expect as an outsider.
When the foundry sends you a design kit which contains all their design rules and tooling around a process, then this process has some codename that appears everywhere (think filenames, names of library elements, and so on). This codename tends to be something like GF14 (for GlobalFoundries' 14nm) or N7 (for TSMC's 7nm) plus cryptic suffixes for different revisions of the foundry process.
So the 14/12/10/7nm terms are actually part of the design engineers' everyday work flow. They just also filtered through to marketing for whatever reason.
I could imagine that at some point in the future, foundries will switch to a year-based versioning similar to what happened with a lot of software. So you'll have a GF2027 process and so on. That's pure speculation on my part though, and inertia is definitely a thing.
When the foundry sends you a design kit which contains all their design rules and tooling around a process, then this process has some codename that appears everywhere (think filenames, names of library elements, and so on). This codename tends to be something like GF14 (for GlobalFoundries' 14nm) or N7 (for TSMC's 7nm) plus cryptic suffixes for different revisions of the foundry process.
So the 14/12/10/7nm terms are actually part of the design engineers' everyday work flow. They just also filtered through to marketing for whatever reason.
I could imagine that at some point in the future, foundries will switch to a year-based versioning similar to what happened with a lot of software. So you'll have a GF2027 process and so on. That's pure speculation on my part though, and inertia is definitely a thing.