It is, and that's part of the point. Marriage is not just looking after children.And having a child isn't such a responsibility?
Clearly the oncoming baby will not be left wanting - there's a close-knit extended family right there. The boy and girl simply didn't demonstrate sufficient ability to take on the responsibility of marriage (they sound thick as bricks, frankly).
However at the end of the year, that issue will be entirely moot. They will turn 18, become legal adults, and new rules will apply.