Customisation in the form of additional abilities is very much a case of the illusion of choice. There's quite a few abilities that are a 'must have' and are objectively much better than their counterparts, so by allowing everybody to access the entire list the overall game is more balanced.

In-depth customisation for abilities works much better in single player games rather than in multi-player games where the expectation is going to be to use the 'best' abilities for the sake of efficiency.