Eg when we post a senior eng job on eg glassdoor, stackoverflow, or linkedin, we are deluged with resumes. Just the ad easily costs $250. Then we get applications who ignore that we don't sponsor visas, clearly don't have the skills required (6 year SAP programmer who wants to be a senior fullstack eng? No thanks), or are junior eng trying to make a huge jump. 1.5 years experience does not make you a senior SE who can be trusted to design and land large features with minimal oversight.
The first problem is an eng manager reviews all those resumes. It easily requires 10 minutes per, including writing nice rejection letters. And that's just for inbound. Outbound can take 30+ minutes per.
If someone passes the resume filter, we do a phone screen with one of our senior eng shadowed by a junior. A 45 minute call plus prep plus decision afterwards costs me 2 hours of eng time.
If you come in, we do about a 3.5 hour interview across 6 people. We cover travel expenses and lunch if an interview runs over lunchtime.
The whole thing easy costs us $1.5k, plus tons of eng time. And that's if we source. If a recruiter sources, we're looking at 20%.