I’ve always read they were interested, but didn’t have the ability to pay Urban the amount he wanted.
I too would contest the assertion that the fall had to do with internal decadence. However, I would say that civil strife and internal squabbling did play a large part of the decline.
Of course, the crusaders of the Fourth Crusade didn’t really help too much, either.
The Fourth Crusade was indeed an abhorrent act. When was it? 1202 to 1204.
It is false to blame the fall in 1453 on something 250 years before is rather like blaming 9/11 on weakness caused by the French and Indian War.
It makes as much and more sense to blame the fall to the Ottomans on taking of the city by Michael VIII in 1261. That was 50 years closer in time to the Fall than the 4th Crusade. What had the Palaeologi done for the last 200 years? If they were not going to do anything, why not let the Latins keep it? Why not work with the Latins, or if they had to take the city, why not emulate the Comemneni to fix the weaknesses and retake the lost territories. The Comemeni did that in only 4 years.
Rather than that, the Palaeogi and their apologists blamed others for their inaction and their failings.