The debate helped to reveal several potential problems with Harris’s strategy:
The fact that your policy positions closely resemble those of voters on average doesn’t necessarily mean they reflect a lot of voters’ first choice — and being voters’ first choice is how you win primaries. On health care, for instance, there might not be that many voters who prefer Harris’s compromise approach to both Biden’s public option and to Sanders’s purer form of “Medicare for All,” each of which are fairly easy to explain to voters.
The media tends to frame policy arguments between the candidates in a way that maximizes conflict. If you don’t clearly stand on one side or another of that conflict, you won’t get as much media attention, which, other things held equal, is a valuable resource in the primary.
If you get too cute in tailoring your positions — as Harris has done on some issues — you may develop a reputation as being too triangulating, or as flip-flopping, or even as being less “authentic”3 than candidates whose positions are easier to place into a neat ideological box.