There’s more to be puzzled. Unquenchable fire does not mean eternal fire. The correct way to interpret the meaning of a word is by its usage (compared with the other methods of etymology and definitive lexicons). So we ask a question: Has the phrase “unquenchable fire” used before? Did it mean “eternal fire”? The answer is that it has been used before but it did not mean eternal fire. Here is a famous excerpt proving this usage in the Bible itself (I reject any usage of the word outside the Bible because the Author is not God. God does not change from the meaning of the phrases which He inspired by His Holy Spirit. One Author Who meant One meaning)
Why does the Bible say that the wicked will be destroyed with unquenchable fire?
Unquenchable fire is fire that cannot be put out, but which goes out when it has turned everything to ashes. Jeremiah 17:27 says Jerusalem was to be destroyed with unquenchable fire, and in 2 Chronicles 36:19-21 the Bible says this fire burned the city “to fulfill the word of the Lord by the mouth of Jeremiah” and left it desolate. Yet we know this fire went out, because Jerusalem is not burning today.
To quench means to extinguish or put out. No one will be able to put out the fire of hell. That is the strange fire of God. No one will be able to escape from it by extinguishing it. Isaiah says of that fire, “Behold, they shall be as stubble; the fire shall burn them; they shall not deliver themselves from the power of the flame: there shall not be a coal to warm at, nor a fire to sit before it” (Isaiah 47:14). After it has accomplished its work of destruction, that fire will go out. No one can deliver themselves from its flame by putting it out, but finally not a coal will be left. So say the Scriptures.
P/S: There’s NO verse which proves that the duration of the “lake of fire” is eternal. Only the punishment of the Devil in the Lake of fire is described to be to the “ages of Ages”. Thus we deduce that the maximum possible time (subjected to the worst sinner = Satan) itself is limited in time in the lake of fire (to the ages). Hence, it is not eternal. That God saves all men (1 Timothy 4:10 highlights that even showing the difference between “all men” and “believers” in the same verse) and God saving the whole world can be deduced from other verses (1 John 4:14, Acts 3:21, John 3:17, Colossians 1:20 etc). This is not deviated teaching as even the earliest history of the majority of the earliest church records. Four out of six theological schools taught this (literally).