If wages are growing for this group, then it stands to reason that costs of joining this group should also be also rising. Economically speaking, there cannot be a disparity where simply having a tertiary education leaves you better off than not having it. If there is, then people will join that group, driving up costs and negating the disparity. The economy always finds equilibrium given enough time.

It's a similar situation to housing. As an advocate for lost-cost rural living, I have asked a lot of people why they choose the high-cost city. The answer is always the same: Their higher paying job justifies the higher cost of living. And thus living costs are rising to reach equilibrium with rural areas. There, again, cannot be a financial advantage to living in the city, else people will move there, drive up costs and negate the disparity.

Any time wages rise for a particular group, costs have to as well. It is the only way the balance will remain in the economy. The exception is when you don't let all people join that group. Without access, then people cannot move to find that balance. There is why everyone who is ultra-wealthy are so due to exclusive property rights (land, intellectual property, etc.) that are out of reach to everyone else.