User blog comment:Xilinoc/Ch. 610 - Mausoleum of Skulls/@comment-25897574-20141220034850/@comment-5398287-20141220051422

Yeah, Haschwalth stated in 565 that it was pretty obvious Uryu only joined to avenge his mother, which is why Yhwach put him in a position where it was all but impossible to betray him without consequences.