Are they too irrational to talk to each other? Maybe, but they each have something the other wants:
Comcast has the rights to characters Marvel would like to use in their MCU (and if Disney doesn't deal, Comcast could play "keep away" for the next 30 years or more).
Marvel/Disney has the expertise and the ability to increase the value of those characters by integrating them into the MCU plus Disney has control of merchandising etc.
Since they both have something the other wants, it's possible to come to an agreement. If one side feels they have a better position than the other, that could shift the balance to one side or the other, but it shouldn't prevent a deal.
For example, here's a hypothetical deal: Marvel produces two films per year for Comcast featuring characters from X-Men, FF or some combination with those characters existing as part of the MCU. Comcast pays all the bills, and Marvel gets 10% of the gross (no matter how much the films make or lose). Marvel gets the rights to integrate any characters they want from the X-Men or FF into their own films with no limitations.
I think that might be a good starting point, but lets say Comcast likes the deal but Disney doesn't. Okay instead of 10% of the gross, Disney gets 15%.
Or conversely, lets say Disney likes the original deal but Comcast doesn't. Go the other way and instead of 10% of the gross, Disney only takes 5%.
So it's just a matter of sliding the numbers around until both sides are willing to sign that deal.
Of course if both sides are too stubborn to talk (as seemed to be the case with Fox), it still might never go anywhere, but I believe if both side act rationally, something could be worked out for mutual benefit.