Why is it that political parties have no interest in reeling in their members who need some time at the crazy bank?

Assuming you're talking about the United States: while the views of zealous ideologues within both the Democratic and Republican parties may be extremely unpopular among most American citizens, these are the people who tend to actually vote in droves in primary elections, and most places in the country by now are strongly "red" or "blue" in culture. The emergent rule in more districts than not is thus: go moderate, get primaried.

Obviously that is not the only reason, but it is a big part of it.

No publicity is bad publicity I guess.

Republicans.