The problem is the market is quite small. They seem to manage with the ATRs in Ireland, albeit with a few incidents now and again. I believe these may have been down to inexperienced crews though.
The Saabs are pilots aircraft but the ATR is more economical and passenger friendly. Fuel burn of probably 800kg/hr with 72 passengers.
The smaller Dash 8 models would have been a good replacement for the Saab 340 but they stopped making them too. The Q400 wouldn't really be suitable for Loganair's shorter routes.
The Saab 2000 will be expensive to operate long term.