The issue is that defining VSE for the multi-winner case is, uhh, complicated. In particular, PR doesn't do a good job of satisfying VSE under the most intuitive model, one where voters' utilities are additive, i.e. satisfaction equals the sum of scores you assign to each candidate. If that was actually the case, the best methods would be winner-take-all (pick the candidates with the highest scores).
The ideal situation would be to have voters score each set of candidates, e.g. "a committee with A, B, C has a score of 3; one with A, B, D has a score of 5, ...". Then we could maximize the sum of scores. However, that's completely impractical for voters, it's difficult to model utilities, and a method like this would be extremely vulnerable to strategic exaggeration.
So, in the proportional context, so far we've found it easier to just deal with pass/fail criteria rather than VSE. That's not to say VSE couldn't be extended to the multiwinner context, it's just that it's complicated and we don't know how yet.