[Did the flames melt the steel beams? If not how come?]
Helps to have a hundred tons of jet fuel to help the process along. Plus this is a conventional design, with thick steel beams, not the hollow ones used in the World Trade Center. That is why they reverted when they built the new WTC. The design that collapsed might have been uninsurable. Another issue with the old WTC is that they left out the asbestos cladding for the steel beams that was part of the design because of OSHA rules. If used, it might have protected the buildings from collapse. I doubt China worries about asbestos.
https://apjjf.org/-Melody-Kemp/3332/article.html
The fire proofing put on buildings in NYC is meant to last for two hours. Both building lasted just under that notably the South Tower which collapsed first because it was struck at and angle.
What do you mean by ‘’hollow beams’’?