If the hiring process is a significant burden to the candidate when compared to your competitors, it might become, even if not formally recognised.
This is why I asked if you can detect any interesting signals in your candidate’s profiles that diverge from the overall candidate pool (hard to get stats on the people who don’t apply, but I think you understand where I’m going).
For the record, I’d LOVE to see that kind of data.
You're conflating a couple of things here -- while we don't select for enthusiasm as such, we very much do select (both implicitly and explicitly) for intrinsic motivation. (So the signal of candidates that choose not to apply is not only hard to get, it's also not necessarily interesting.) In terms of where that intrinsic motivation comes from (which is perhaps what you're asking?), we have found that it can be found in a wide variety of places and backgrounds. And indeed, such as there's a common theme at all, it's that it doesn't necessarily follow from a resume.
You touched a very good point - in order to apply, the candidate must be very motivated to apply. Unlike, say, the hundreds of random resumes we (present employer) get every day (feels like a DDoS attack sometimes) - those candidates are motivated enough to fill out a form, but not enough to read the job posting.