Why do we love Prog concept albums?

The great thing about thing about being from a certain vintage is that sometimes you are a witness to events at the time they happened, even events that happened 43 years ago. The hard thing is trying to keep things in perspective for other people if they were around at that time or not as after events coloured the original. Case in point, Aqualung as a concept album. When Aqualung was released in 1971, ITCotCk was two years old and the definitive concept album Pink Floyd's Dark Side Of The Moon was still two full years away from putting it' s "Concept" stamp upon the Progressive Rock world. And that is a key point to remember as Dark Side revived and improved the past "concept album" practice of instilling a sense of continuity to the listener by running all of it's songs together. Either by cross fading one song into another or bridging the songs together with sound effects like off hand dialogue and ticking clocks and other sound effects.1971's Aqualung used no such aural tricks to instill a sense of continuity of theme.

In the album's liner notes (the upper half of the back cover) was a preamble that linked Anderson's "4 songs with a common theme", as he stated in your post, i. e. religion, with the man made subhuman species of which the Aqualung figure is a part with both the subhumans and and man's created "God" having within both an unforeseen divine presence. To wit:

1) In the begining Man created God; and in the image of Man created he him.
2) And man gave unto God a multitude of names, that he might be Lord over the earth with it wa suited to Man.
3) And on the seven millionth day Man rested and did lean heavily on his God and saw thtat it was good.
4) And Man formed Aqualung from the dust of the ground, and a host of others likened unto his kind.
5) And these lesser man did cast into the void. And some were burned; and some were put apart from their kind.
6) And Man became the God the he had created and with his miracles did rule over the earth.
7) But as these things did come to pass, the spirit that did cause man to create his God lived on within all men: even within Aqualung.
8) And Man saw it not.
9) But for Christ's he he'd better start looking.

This is what started Aqualung's concept album debate upon its release in 1971, not ghost whispers. So even if Anderson still contends to this day that Aqualung is not a concept album, his Book of Genesis mocking album preamble connected more than  just four songs and themes together such as Aqualung, Crossed Eyed Mary and the entire side two multi song diatribe on Man's "God", infinitely better than Dark Side would two years later on with sonic tricks.  The difference between the two albums is that one album's creators agree that theirs is a concept album, the other album's creator does not. And Ian Anderson is still having a chuckle over it at our expense, cheeky devil, as far as I'm concerned. Better get his mum to start writing that note.