you did not see it in the program Nana, but to get the blokes to a point of trust enough that thy would meet you can takes weeks if not months. They need to groom the "victim" and evidence of that grooming needs to take place and be recorded. You cant just go online and say "yeah, i'm 11, wanna meet?".
You need to be online evenings and weekends to respond. Do you know how much it would cost to employ someone (or a team, because it requires a team) to be on duty all the time like that? Plus the paper work and evidence trail. The preparation of the case for CPS. It is a huge undertaking for a law enforcement agency. You cant be an 11 year old online only 9 - 5 or on a shift pattern, and you cant share the role because you need an airtight alias or the criminal gets spooked.
There are people out there doing this, but as i said often (not exclusively!) the money and resources are put into finding the bigger fish, as it were, rather than goading people on 18 plus chat sites into revealing they really like younger girls. There just isn't enough money to do it.