Pretty clear the retirements of so many of the “old bulls” particularly in the House, but also in the Senate is a result of polarization of the bodies and inability to find common ground on nearly any issue.
Blame goes to both Republicans and Democrats for failing to put the national interest above parochial concerns and partisanship. Having said that, the GOP/Tea Party class of 2010, who’s primary objective is to prevent government from functioning, deserves the lion’s share of the blame.

Another thought: he’s been there twenty years.  That’s a decent amount of time.  A career politician who has had a career of it.  Whether or not he thinks things are getting done.  (And we see his post-retirement acting round about here, where he has no need to cow-tow in any direction, and so, raises the debt ceiling.  Though, I doubt he was ever in the need of sitting in “catch and release” mode for Boehner in rounding up the necessary Republican votes while letting Republicans stay to the right as need be…)

Possible Republican replacements for Hastings include state representatives David Taylor and Brad Klippert and state Sen. Curtis King.