Bart Ehrman's irrational faith (in Q)

If you've been following this blog for a while you might remember the '$1,000 Challenge to Bart Ehrman'. The focus of this challenge was whether Bart Ehrman had a specific reason for thinking that Matthew did not copy Luke. At that time Bart declared himself "completely convinced" by an argument offered by Mark Goodacre - even though this was an argument that didn't address the question of whether Matthew used Luke. 

A few days ago I tried asking a related question in an AMA with Bart Ehrman:

Robert Derrenbacker recently wrote:

"[I]f, for the sake of argument, one were to dispense with Q and maintain Markan priority, Matthew's use of Luke (as advanced by the supporters of the MPH) actually makes the best sense of the material in a Mark-without-Q scenario."[1]

Do you agree that Matthew using Luke (with Markan priority) is a more likely solution to the Synoptic Problem than Luke using Matthew?

Bart's full answer can be found in the clip posted above. The original context is Reddit/AcademicBiblical/BartEhrman-MatthewAMA

The arresting thing about this answer is that (after explaining the Q Theory) Bart offers a reason why he thinks Luke did not use Matthew. What he does not do is offer a comparable reason why Matthew could not have used Luke. This is, however, not surprising. The mechanics of Matthew's use of Luke are a lot like the mechanics of Matthew's use of Q - (which explains the initial quote from Robert Derrenbacker, an established Q scholar). Bart does not have a problem with the way Matthew is required to use Q, so it is understandably difficult for him to offer this type of reason why Matthew could not have used Luke. 

So far my questioning of Bart Ehrman has produced bold and confident statements that Matthew could not have used Luke, but without an explanation of the basis for that confidence. "Nobody thinks that", is not enough. And, without a rational basis for believing that Matthew could not have used Luke, Bart has no rational basis for believing in Q - a hypothetical entity in which he, nevertheless, continues to have faith.  

See also: Swinging big and swinging blind: Bart's extra gamble

[1] Robert Derrenbacker Jr., '"Unfinished" Mark "Replaced" by Matthew and Luke? Some Recent Studies and their Implications for the Synoptic Problem', in The Synoptic Problem 2022: Proceedings of the Loyola University Conference, Olegs Andrejevs, Simon J Joseph, Edmondo Lupieri, Joseph Verheyden (eds) (BiTS 44, Peeters, 2023) page 193.