First let someone define the shidduch crisis and state how kollel causes it, then we’ll talk.
As I said earlier, Kollel (as defined by people in their 20s sitting and “learning” (or hanging in the CR, etc.)) does NOT cause the shidduch crisis (as defined by the burning need for many young girls (let’s say ages 19 – 23) to get married, and the consequential large group of older singles). It is the strong desire of girls to marry and ONLY marry the type of boy that will be in “kollel” (as defined) that is theorized to be a strong cause of the shidduch crisis (by any definition). Put it under the “pickier girls” theory.
The outcome of that desire is that when the boys see that girls (or more accurately, the Shvers) are willing to support them, they also realize that it would be stupid of them not to go to “kollel” (as defined) and get a honeymoon with no real responsibilities. For a Bochur, it is like being in Beis Medrash as before but “with benefits”, such as someone to cook meals and a place to impress single bochrim.
So if anything, the shidduch crisis causes Kollel! (a cynic would say this is a planned outcome)
This certainly is speculation, but the theory happens to fit the facts.