Why no issur hana'a on leather from non-kosher animals?

Question

In the second perek of Maseches Pesachim, there's a sugya dealing with a machlokes between Rabbi Abahu and Chizkiya regarding whether there is an issur hana'a in addition to issur achila regarding all foods that the Torah made assur through lashon like lo tochelu, to tochel, etc. - with certain exceptions such as neveilos or gid hanashe for which the Gemara learns out that there is no issur hana'a despite such a lashon being applied to them.

See the beginning of this sugya in Pesachim 21b :

וּפְלִיגָא דְּרַבִּי אֲבָהוּ. דְּאָמַר רַבִּי אֲבָהוּ: כׇּל מָקוֹם שֶׁנֶּאֱמַר ״לֹא יֵאָכֵל״, ״לֹא תֹאכַל״, ״לֹא תֹאכְלוּ״ — אֶחָד אִיסּוּר אֲכִילָה וְאֶחָד אִיסּוּר הֲנָאָה (מַשְׁמַע), עַד שֶׁיִּפְרֹט לְךָ הַכָּתוּב כְּדֶרֶךְ שֶׁפָּרַט לְךָ בִּנְבֵילָה

It seems that the halacha follows Rabbi Abahu, see for instance the Rambam's Mishne Torah, hilchos maacholos asuros 8:15:

כָּל מָקוֹם שֶׁנֶּאֱמַר בַּתּוֹרָה לֹא תֹאכַל לֹא תֹאכְלוּ לֹא יֹאכְלוּ לֹא יֵאָכֵל אֶחָד אִסּוּר אֲכִילָה וְאֶחָד אִסּוּר הֲנָאָה בְּמַשְׁמָע עַד שֶׁיִּפְרֹט לְךָ הַכָּתוּב כְּדֶרֶךְ שֶׁפֵּרֵט לְךָ בִּנְבֵלָה

Yet, we see people having no issue with a wide range of products from non-kosher animals (i.e. animals that were prohibited through a lashon of lo tochel, lo tochelu, etc.) such as leather (consider for argument's sake leather from an animal that is itself treif, such as a pig, rather than a neveila or treifa of a kosher animal like a cow).

Does this not run contrary to the halacha prohibiting hana'a from these animals?

Answer 1

I found a couple answers:

• The רשב"א in שאלות ותשובות 3:223 points out that the Gemora's answer on 23A for שרצים applies to animals/birds as well. See https://www.hebrewbooks.org/pdfpager.aspx?req=1378&st=&pgnum=145

• The Pnei Yehoshua to Pesachim 23A says that the Gemora didn't ask about animals/birds because animals/birds are assur even while they're alive, and as the gemora already proved live animals have no issur הֲנָאָה , they couldn't later gain an איסור הֲנָאָה, due to the principle of אין איסור חל על איסור.