I'm not sure it's confirmation bias, but if it is multiple people have had the same experience.
For the last two jobs I got by actually actively seeking out an opening rather than being contacted by a recruiter, I only send out 2-3 applications each, but with a cover email that was custom to each company.
On one occasion I had a 100% interview rate, on the second one a 66% one (1 out of the three companies had an automated screening system and I'm pretty sure I was too expensive for them).