First...It is a false argument that aviation fuel cannot get hot enough to melt steel. Certain conditions, like the afterburner of a jet engine, has temperature hot enough to melt steel...
Afterburner Basics
The temperature here is in the flame, has an exit path and that is why this section of the jet engine is immune to that high temperature.
Second...These columns are load bearing, or more specifically,
VERTICAL load bearing. That mean there is no need for any fire source to reach four-digits temperature. Look at the blacksmith below...
A section of the steel bar is hot enough to be pliable with hammer strikes but still retain its general shape. Another section of the steel bar is cool enough that the man can touch it with his bare hand. So for a steel column that has a vertical load, all the fire has to do is heat up a section of the column soft enough and let gravity do the rest.
Third...Steel expand when heated...
Thermal Expansion Expt
This is on a hot summer day, probably around 100-104, nothing unbearable. But these steel structures warped anyway. Each segment curved because it had nowhere to go. For the WTC steel columns, the ones that got heated also had nowhere to go. This is compounded by the fact that unlike railroad tracks, the stress (vertical) they bear are tons and it is constant. Gravity does not let up, except in the alternate universe inhabited by loony 9/11 conspiracy theory believers.
Finally...We have a combination of severed columns and heat weakened columns. For the remainder that are structurally intact, there is now lateral stress they have to bear that was not there before.
None of these individual factors will collapse a structure but a combination of them will and that is how we collapse a condemned building. We compromised a few strategic internal structures and let gravity, aka vertical load stress, do the work. An aircraft severing a large number of columns in this 'matrix' of columns is really no different than if we had placed shaped explosive charges on them.