Ah, what the fuck, misclicked on something and this came up.
Anyway, I think it's because prog had a desire of a journey, there are very few shorter prog songs. And the best moments have to be the first track, to truly grip you onto the album, and the last one, to release everything as one grand burst of emotion. Hence why in quite a few prog albums the first and last tracks are the best.
Here's another one that fits the bill.