Kobayashi did it spectacularly in Suzuka last year
Anyway, I think it’s because of the turbulence and the heat coming out from the rear. Cars cannot get as close nor can they slipstream and get a tow.
Also, on the supposed ‘block pass’, I would like to quote Senna: “If you no longer go for a gap that exists, you are no longer a racing driver”
The point of outbraking is, you brake to the speed capable of turning in a corner without running wide in a shorter time period. Because it depends on whether your car is grippier or you simply have better car control, it’s not ‘unsportmanlike’.