Imagine Pogacar and Roglic had not left a huge impression this year, winning their GTs but not being the talk of the town, van der Poel wouldn't have done the Tour and Powless would have won the world championships... I think van Aert would have a pretty good shot at the award this year.
Ala won Strade, MSR, FW that year, two Tour stages, stages in all his stage races before the Tour, and had the yellow jersey for two weeks. If there was a dominating rider of 2019 it was him, not Bernal or Roglic, so no wonder they held him high.