They aren’t?
I will suggest that the Old Testament was written in Hebrew, and Jews may be considered the experts on the Old, and they don’t think the two are compatible.
I can recommend this excercise to you: Take a weekend with a good translator’s Bible and go through Matthew and actually compare the Greek text of “fulfilled prophesy” to the Old Testament Hebrew words that are referenced.
They normally work pretty well in Greek, but not in Hebrew, which shows that “Matthew” wasn’t Jewish, and was trying to convince Greek speakers ignorant of rabbinical training that there was a Old Testament prophesy.