Being able to sell yourself during a job interview is not necessarily a good indicator of your ability to communicate effectively at work. Instead it selects for people are shameless self-promoters.
I never suggested that it was. I'm just saying it is a skill to being able to promote yourself. Hiring based on a skill (even if it is only semi-related to the job) is hiring based on merit.
Also, if you can sell yourself you are likely to be able to sell ideas which is a good skill for developers to have.
Depending on the work, it may be more valuable than coding ability even. You need people with the right ideas that can win arguments. Without that you can only build garbage.
Programming skills would qualify as merit but so would "social and communication skills". Hiring based on any of those skills would still be hiring on merit. Having an immutable characteristic like a specific gender or race is not a praiseworthy quality.