Why pair gas turbines with electric drive?

Why use gas turbines to feed an electric drive train instead of a direct gearbox?

Electric drive can combine turbine and diesel generation while supplying other ship systems, although direct gearing remains viable and may favor top speed.

An electric arrangement lets diesel engines and gas turbines feed a common power system rather than share one mechanical gearbox. The generating capacity can then support other shipboard loads as well as propulsion. A direct gearbox remains possible and may produce a different maximum-speed result. Electric drive is a useful distribution option, and some installations would still favor mechanical gearing.