Black Mesa likes the human touch that only a guy in a HEV suit can provide.
They're very old-school. It wouldn't have felt the same had it been entirely automated.
Don't forget that technically, this was a decomissioned bunker/missile silo from the cold war times. Perhaps the electrical installation wasn't expansible enough and didn't allow to move the button(s) to a safer location, and it was out of the budget to redo it appropriately.
And they bought Cyrix!