Could be #2. Also could just be case-by-case decisions.

#2 could make some sense even if these assistants have a very high opinion of Kelly, just because he's creeping towards that 10 or 11 year wall where even the best ND coaches have historically burned out. With that in mind, maybe this is a good offseason for an assistant to "sell high" after a season in which the coaching staff got a lot of praise.

From reading some of the info on this board in the last few days, it's been speculated that A&M came back with a ridiculous 2nd offer for Elko after ND matched the first one. And that returning to the NFL may have always been in Hiestand's plans, partly motivated by the ability to get an NFL pension (I don't know exactly how that works, I'm just repeating what another poster speculated). If there is merit to both of those theories, then maybe it's just "shit happens" with no alarming common theme.

If Kelly had a better track record of consistency during his 8 years, then there'd be more of a "ho hum" attitude towards staff turnover.