And so does fire ... steel significantly weakens well below its melting point...
The twin towers were built with economy in mind and some of those trade-offs made them even more vulnerable to fire than some other very tall structures, such as the Empire State building or the Willis (formerly Sears) Tower.
In particular, the twin towers had large open floor plans with minimal steel used with minimal fire protection compared to that of buildings utilizing box construction, such as the Empire State building, which contains more steel, much of which is well fire protected, than both of the taller, more spacious twin towers combined!
Once one floor fails, it pancakes on to the one below it, which in turn fails due to that extra mass on top of it, followed by more pancaking rapidly leading to building collapse.
Placing explosives would be far more difficult than people realize - sure it doesn't take much, relatively speaking to bring down a building, but one can't just place them haphazardly. The amount of time and effort required would have been considerable, as well as very noticeable, especially if placing them so high into the structure.
I'm amazed what people believe and post without at least thinking it through a bit first. But then this is GFY so perhaps that's par for the course
Ron