Those same computer repairs can be done remotely.

A number of them can't be done remotely - especially if it's not just simply a computer repair.

Or you have a mechanic on board for repairs, just not driving the train.

Essentially, the driver often serves as half a mechanic. So, at that point, he might as well drive the train (or at least survey the system, making it either GoA 2 or 3 ).

Besides, trains already have a dozen crew anyways

Except they don't. The number of crew is constantly being reduced - in fact, self driving trains themselves are a crew reduction method. In fact, most self driving trains don't have any crew along in the first place.

No need to risk lives when we don't need to.

Except it's far from clear that we're risking lives, see above.