late reply, but I know for Google they're required to start participating in interviews to be promoted to L4 (?) and above, whether they have interest in it or not. Maybe there is a disproportionately harsh performance penalty for recommending someone for hire that shouldn't be hired, vs the other way around, and the easiest way to "tick the box" for the promotion is to do the interviews and reject everyone (unless they're seriously impressive).
I've experienced this as my company recently implemented metrics for code reviews, with one of them being "percent of lines commented on during a code review"; which unfortunately makes me comment on lines that I wouldn't usually do just to serve the metric.
I'm wondering if they have a similar thing.