Ignoring the factual issues (JSA and CA?) and judginess and answering only the title: A combination of poor employment prospects and doing the bare minimum.
I was on JSA back in 09/10. It was the depths of the recession, I couldn't relocate, I didn't have my own transport, and the longer I'm unemployed for the worse I look to potential employers. I was also a lazy fucker who'd do the minimum required job applications the day before signing on (something I don't think today's JSA claimants can get away with). The upshot is that over about a year of claiming (not continuous, I get a temporary job for a bit) I could count the number of interviews I got on one hand.
Oh, and the only reason I wasn't in crushing poverty and facing homelessness was that I had support from family. JSA is a pittance, and a pittance of a pittance for the young, and you're lucky if Housing Benefit even pays for the full rent.
Although the job market's improved since then, I still feel that it's in the interests of the rich and powerful to keep it an "employer's market" where many people must chase few jobs and finding work is hard, because that means employees won't risk losing their jobs over little things like laws and ethics.
Fast-forward a few years, and a friend of mine has been dismissed from one job for misconduct and didn't last a month in another before he was sacked for always being late. Unsurprisingly he's found it very difficult to get work, he's had some temporary and seasonal stuff but nothing ongoing.