From what I understand, it’s not so much their skills as an informant/agent provocateur that’s appealing, as having them firmly in the pocket of the alphabet agencies. Knowing your handler can single handedly ruin your life (as credible allegations of paedophilia probably would) is one hell of an incentive to stay on their good side and do their bidding, as a matter of self-preservation. Knowing your agent is likely not gonna flip (like a lot of CIA/FBI did in the early Cold War) helps too.

Some may have desirable traits that doesn’t necessarily involve skill. And this goes for any criminal with a potentially hefty sentence.

For example, cartel drug dealers get turned because they may face extradition and are close with king pins. Some hackers or businessmen may be unremarkable but they control important illicit marketplaces which could net more gains for Feds. Pedos may be good at manipulation or simply have the means to procure children to compromise other targets. The BLM infiltrator the in my OP lied about ever serving in militias and fighting against ISIS. He was just a grimy, loud, violent asshole whose presence was intoxicating to the activists.

Regardless, the usual commonality between all of them is that their lives could be ruined, deservingly or not.