God does ALL things to glorify himself and to benefit His people.
I follow the doctrine because all scripture is relevant to believers today! All things in the OT are extremely important to understand because they were written for our benefit by providing examples and instructions for us (Rom 15:4; 1Cor 10:6, 11; Heb 4:11; 2Pet 2:6; Jude 7).
Furthermore, God did these kinds of thing a lot more than three times. Even if we stick with just Judas and the 5 persons mentioned in Rom 9, you forgot Ishmael. Why, oh why, did poor innocent Ishmael not receive the inheritance?

So, with Ishmael included, we're now up to four examples.
Plus..back in August I wrote two posts proving from both Special and Natural Revelations that divine "determinism" is alive and well! In fact, the very first place in scripture we see this "determinism" played out is in Gen 3:15 when God determined to save Eve and also determined to not save Adam! But before you rush off a lame, knee-jerk, crazy, visceral retort about poor ol' St. Adam, answer this question first: T
o which of the two seeds did God consign Adam?