I too think there is a crash coming but not for complicated reasons that require advanced economic theory.
I think the explanation is so much simpler: we collectively lose our minds. During the dot com crash, it wasn't that Internet companies were awful like we thought they were when we panicked. It's that we collectively lost our minds during the gold rush for anything with dot com in the name as a get rich quick scheme.
Same with 2008. We thought real estate mortgages were a get rich scheme and panicked when we found out that we collectively lost our minds and put millions of people in houses who couldn't afford them yet. Only a few people like Warren Buffet seem to be able to keep a level head and neither panic nor go nuts over easy money.
One reason I think a crash is coming is because of articles like this one that help create the fear that after a boom there must be a bust for some fuzzy reason that isn't elaborated in the article. Another is the never-ending search for a get rich quick scheme, something easy and we'll all prosper. A tax cut. That will do it.
Lifting ourselves out of a crash like 2008 takes years of hard work, just like building a real dot com company or earning enough income to buy a house does.