It's possible that they knew they were either losing access (perhaps a vendor update or action was going to break access) or that news was going to spread due to some upcoming legal case. In that case they might try to get as much impact as possible, especially if they were in position to monitor what spooked users tried to switch to or whether they started communicating to previously unseen partners.

The users aren't that stupid. If the police have been quiet for months and suddenly start busting many different gangs by doing raids that would have required information only a few gang members had, it doesn't take a genius to figure out that the common thread is the use of Sky phones.

Once they start exploiting intel like that, it won't take long until the jig is up, so coordination and mass action becomes essential.

Only true if they were confident they could keep mum about the hack. Someone in law enforcement could leak it to the criminals, SKY could find out, etc...