FAS don't run the CSCS schemes, they & FETAC award the certification at the end. There are training companys all over the country running CSCS courses, who then apply to FAS for the CSCS cards.
The reason is probably because it costs the individual so much to attend one of these courses and an instructor requires a minimum number of attendees for each course. Not many people will spend E1000 on an excavator 'ticket', for example, when there is no work for them at the end of it. Remember, there are thousands out there with CSCS cards for various disciplines who have plenty of experience and yet are twiddling their thumbs.