Why is wood different? TB Beitzah 33

Previously we have learned the principal that once something is permitted for the purpose of food preparation on the Festival it is also permitted when not performed for these purposes (מִתּוֹךְ שֶׁהוּתְּרָה לְצוֹרֶךְ הוּתְּרָה נָמֵי שֶׁלֹּא לְצוֹרֶךְ.). The classic example is carrying. Since you’re allowed to carry for food preparations, you are allowed to carry everything else that you need for the Festival. Today’s daf TB Beitzah 33 provides us with wood as an exemption to this rule. One is only allowed to use wood as firewood and nothing else. “And one may not prop a pot that does not stand straight with a piece of wood, in order to prevent it from falling. And similarly, with a door. And one may not lead an animal with a stick in the public domain on a Festival (Mishnah on TB Beitzah 32b)…The Sages taught: One may not prop a pot with a piece of wood, and similarly a door, as wood is to be used only for kindling. With regard to any use other than kindling, wood is considered muktze.” (Sefaria.org translation)

The Rishonim have tried to discern the under pinning reason for this exception while accepting Rashi’s explanation that the word is considered muktze. Rabbi Zarakhia Halevi holds that the prohibition of muktze on the Festival flows from the principal that the rabbis forbade something on the Festival because of Shabbat (less the person draw a wrong conclusion and think it is permitted also on the Shabbat). Only those things that are forbidden to use on Shabbat are also forbidden on the Festival because of muktze. Since firewood is forbidden on Shabbat because one may not light a fire at all, the rabbis only permitted its use for the unique purpose of food preparation. The Ritba explains this prohibition of muktze lest somebody creates a tool out of raw material.