Kendrick did OK. As would other contemporary headliners who headlined on other days, Dua, Billie E, Stormzy.
SZA just isn't mainstream or well known enough here, I don't think it's generational. The 90s/00's acts that are still big enough to headline now are obviously going to be well known/household names, with more material that hits.
The sad thing is, had they packed out the Pyramid with 90's/00's acts on the Sunday last year, rather than anything contemporary, It would have been rammed.