It's probably because so called centrists don't stand for much of anything beyond trying to gain a social edge by pretending they're above it all when they aren't. It's an excuse to attempt to distill belief systems into a very narrow point of view precisely like you've described with the whole "only reason" nonsense. I'd really appreciate it if one could describe why they consider themselves one since it's totally meaningless to me when someone self identifies as a centrist.
Just like in marketing it's all about how you frame a question to a person. Realistically most people share common beliefs at the fundamental level in what they want to see out of the power structures in our society. In other words, the vast majority of people in this country want to improve upon their material conditions. The rest of the circlejerk is just grifting.
A couple of ideas: (1) Centrism is situational. One might think that the status quo is objectively reasonably close to the ideal, in terms of the general way society is arranged even if there are many imperfections. (2) Centrism is technocratic. If you don't favour a lurch to the left or right, it would make sense to want efficient improvements to how things are run - accepting good ideas regardless of which area of the political compass they come from, bipartisan support for policies on their merits.
Based on the above, centrism (and indeed, being centre-left or centre-right) seems viable as a real belief that people can hold, not some strategy to appear above it all for social benefit, or as a stratagem used by someone actually highly partisan. A centrist's goals could be directly met by encouraging trial of different ideas across the political spectrum, and consistent meta-level rules rather than tribalist thinking. Trying to rise above the bunfighting isn't the benefit of centrist views, it's a necessity to enable the things they want to achieve.
I'll sometimes self-identify as a centrist in that I notice two increasingly radicalized extremes that spend most of there energy screaming at each other. You might think I'm doing that to "gain a social edge" but the truth is I just don't like screaming.
>"...I'd really appreciate it if one could describe why they consider themselves one since it's totally meaningless to me when someone self identifies as a centrist."
Why would they care whether it has a meaning to you. They care about their own beliefs.
Just like in marketing it's all about how you frame a question to a person. Realistically most people share common beliefs at the fundamental level in what they want to see out of the power structures in our society. In other words, the vast majority of people in this country want to improve upon their material conditions. The rest of the circlejerk is just grifting.