At this point, the party doesn’t seem to be paying much attention to what large chunks of their own membership want, let alone what Americans as a whole want in their political leaders; opening up the primaries would (hopefully) have the effect of helping them to focus back on what is important to the electorate. (If you don’t offer voters what they’re looking for, they’re unlikely to vote for your candidate. If they don’t vote for your candidate, they don’t get elected, and you lose the opportunity and the power to shape policy.)
As for instant runoff voting, that too would give the party a lot more information on what voters are actually looking for, while also giving voters a way to express their desires without having to sacrifice their vote in order to do it.
I’ve seen a lot of people–members (or now former members)–who are really disillusioned with the party, and feel both ignored and powerless. That’s not a recipe for success, especially when you add in the part where the party makes up around 25% of voters as a whole, and HAS to have the entire party plus over half the independents in order to win an election.