Criminal services tend to be paid on a block tariff level. You would get so much for a trial or so much for a half-day of trial. Partly, there's a commonality among them. They just tend to be slightly different business models.
Lawyers practising criminal law tend to be more used to that. Lawyers practising in the family area tend to be more used to billing by the hour. That would be the broad reason for it. It's not necessarily so in other legal aid plans, and other jurisdictions outside of Canada do it differently.