There's the general prestige and being the main character every day, but also it's certianly the case that Senate staffers (illegally) do much work for their bosses that they should not be doing. You can't possibly hire elder care staffers who are going to be that attentive to your needs.
That's the kind of thing that happens slowly and then all at once, but leaving the Senate would mean, for some of these people, essentially losing their necessary appendages.
