If incompetent developers do 100 interviews per job, and only last at jobs for 6 months before being fired, and competent developers do single-digit interviews (or 0, getting hired through networking) and stay employed for years at a time, a very small proportion of bad actors can be severely over-represented in interviews.
I've been on your side of the table for a similar role and had the same experience. Literally 20-30 candidates who can't answer basic questions for every 1 who can (and usually the 1 is "just ok").
I think it's just due to the particular pool your company is dealing with. Maybe there is a surplus, maybe there isn't, but you're not able to judge that objectively from your vantage point.
I'm not saying this to be snarky. If you don't have a good answer to this, that probably points to your issue. If you have to think a bit to answer that, it's probably also an issue.
It's pretty simple logic from there.
At my previous company we usually were able to find someone within a reasonable amount of time to fill an open position. One day, HR decided to seize control of the hiring process. They would conduct all of the resume and initial phone screening and then hand us a few "approved" resumes. It became impossible to find anyone after that.
...willing to commute from their home to your premises
...and work with your crazy cargo-cult process
...on your badly-architected, tech-debt-riddled legacy system
...for the crap salary you are offering.