Personal tastes really.
I as a heterosexual male like females. In Yuri both characters are females and thus I as a male enjoy seeing such a relationship being depicted.
In BL both characters are males, i have no interest in males physically or emotionally, therefore I can not feel attracted to BL personally and as such do not enjoy the genre.
Do I hate BL? Absolutely not. I just can't connect to it in any way, but it is a genre that can be enjoyed like any other, just not by me particularly.
TL;DR
I like cute girls, therefore yuri has double the cuteness, therefore yuri is superior.