Well, I just think that it's the way the juries vote - they like radio-friendly, mainstream songs which is reflected on the scoreboards after the juries have voted the last years. I mean, there is a clear pattern in what Sweden's been sending this decade - and Sweden's not the only country that's been awarded by the juries for it. So when you claim "no matter what they song" they send, it's because their songs follow the same pattern year after year, and obviously backed up by top-notch staging.
And sure, great vocals can help, but it's not paramount in order to do well with the juries. I mean, Lake Malawi and Luca Hänni had radio-friendly songs this year with great staging and they came like some points behind Kate Miller-Heidke in the jury vote with the latter having a far superior vocal performance, but perhaps "Zero Gravity" as a popera song was too divisive for the juries as neither "Grande Amore" or "La Forza" killed the jury vote either