Pennsylvania’s current treasurer is Republican Stacy Garrity, who unexpectedly unseated a Democratic incumbent four years ago despite having little funding.
If the party supports incumbents and fights any primary challenger it just means bad incumbents hold office until a Republican beats them due to low turnout.
If we have to vote D no matter what in the general, then noncompetitive primaries take away voters only say in who's elected.
And it sounds very simple but I'll repeat it again:
When Dem voters feel like they have no say, they don't vote. That reduces turnout. And low turnout is the only way republicans get elected to office.