The MAN-ABZ route as you stated is a busy market. BE's flights are often very busy on up to five daily rotations. Perhaps it's performing well as it is and reducing fares to grab a few extra passengers who might otherwise fly BMI Regional wouldn't really serve any purpose.
If Flybe were flying this route with crap loads, then I'd see the need to reduce fares, but generally speaking, it seems to do well as it is.
High load + high fares = PROFIT
High load + low fares = Small profit/break even
Low load + high fares = small profit/loss/break even
Low load + low fares = disaster
The difficulty for Flybe (and every other airline) is finding that sweet spot where you can carry the highest number of passengers paying the highest fare possible.