Runoffs are far from stupid. Suppose that there are three candidates in a race, call them A, B and C, and for simplicity suppose there are 100 voters. Now, let’s say that 40 of them support A, with the other 32 support B and 28 support C. Further, let’s say that if asked for their second choice, the B and C supporters would support either B or C as well. (BTW, this isn’t as contrived as it seems. In most primaries there is an incumbent and one or more challengers. Many voters fall into the “anybody but the incumbent” camp).
Now, without runoffs, we can expect that A would win a primary among these three candidates with 40 votes. However, a large majority (60%) of the electorate would vote for anyone else. Is it really reflective of the will of the electorate that A should just be declared the winner? With a runoff, A and B would be in the runoff. Presumably the “anyone but A” voters who voted for C would switch to B in the runoff. That would give B the 60-40 edge and the primary victory. Isn’t that a better reflection on the will of the electorate than giving the win to a candidate that was opposed by 60% of the voters?
Yes, that does make sense.