It doesn't melt though. In fact mass timber is relatively resistant to fire, possibly better than steel. If I remember correctly, the surface chars and becomes a relatively good insulator of heat, so the core preserves its strength.

Wood really isn't that flammable either. Most thing in your house, furniture, paint, books, drapes etc. is on fire before your walls or your floor. Huge caveat on solid wood walls and floor.

Wood used for construction is required by law to be fire treated.

https://www.fp-supply.com/st-louis-fire-treated-lumber.html

Where? In what contexts? It's not required for houses or town houses where I'm from at least. From the pictures I guess it's mostly relevant to larger buildings?

"Over 90% of the homes that are built in the United States each year are constructed using wood-frame construction"

https://awc.org/codes-standards/firesafety

And close to 100% of those are built with garden variety untreated fir lumber.

This is too general a blanket statement to be true. Plenty of wood in construction is not treated for fire. Fire ratings are generally done for assemblies, not components of assemblies, and there are ways to build fire rated assemblies without treated wood. Also, not all assemblies need fire ratings. Sometimes its just the exterior walls adjacent to neighbouring structures, etc.

wood is a lot less flammable than a material made of chains of hydrocarbons, and has far preferable burning characteristics to plastic.

The two facts that 1) you could burn wood and 2) people build with wood, should not logically lead someone to claim that building things with any flammable materials is ok because of this.