The time is a cost, but at scale any individual target is a pretty minor investment since it's 90%+ automated. Also, these aren't folks that are otherwise highly employable. The opportunity cost to them is also usually very low.
The last attacker I got into a conversation with was interesting. Turns out, he was a 16 year old from Atlanta GA using a toolkit as an affiliate. He claimed he made ~100k/year and used the money on cars and girls. I felt like he was inflating that number to brag. His alternative probably would have been McDonalds, and as a minor if he got caught it would've been probation most likely. I told him to come to the blue team, we pay better.