I feel like we still haven't arrived at an "explain like I'm five" version yet, though?

So maybe something along the lines of... so there's a lot of important things that are different between wood and metals. As u/Lirdon said, metals are just raw elements (i.e. silver, nickel, etc.). The atoms in metals form a special type of bond with each other that's different from the bonds that we see in organic stuff like wood. The type of bonds formed by metals lends itself really well to going evenly from a solid into a melty liquid when you heat it.

Wood is a mix of many types of organic, non-metal compounds. The bonds that these atoms in these compounds form tend to be much, much stronger.

When non-metal stuff with those stronger types of bonds gets heated, sometimes it goes nicely from being a solid to a liquid (like the plastics and waxes that u/tdscanuck mentioned). But sometimessss things get real spicy instead. In the case of wood, the compounds completely break apart into ash, tar, and the CO2 gas. Metals don't really have the option to "break apart" into other things since the nickel, copper, etc. atoms are already in their most basic form.

Maybe? Hopefully the people who actually know chemistry can come fix this lol

Edit: apparently metals can also burn but there's a bunch of reasons when metals common forms we see them don't very often. https://www.wtamu.edu/~cbaird/sq/2018/02/18/why-dont-metals-burn/