While as many have mentioned there was/is no need for more power, another reason for not supplying more to the railway is that electricity supply all over West Dorset is severely constrained and would require lots of money to upgrade.
On another note, First's proposal still had 2tph, one going to London, one to Portsmouth.
Dorset's residents asked for faster trains, and were offered them. Dorset's residents asked for the extra stops at Moreton, Wool, the sheep field by the humpback bridge and the Greenwood Tree to be put back in again, and we were back to square one.