battery cable under the hood, see high current only for seconds
then only see high charge for a few minutes
plus they are exposed to open air cooling from underneath, when the engine is shut down
they are in an enclosed space where the heat will build, but will cool when stopped ( coled from the compartment being open at the frame )
they are not usually called upon to carry a 100 amps for 6 minutes while baking a potato or 80 amps for 10 minutes while making a pot of coffee
or hours of battery charging a bank of batteries (while it could do so)
that #2ga has no problem carrying 40 or 50 amps from the alternator while you drive all day , its usual job
so why is battery cable 2ga instead of 6ga
because 6ga can not be expected to maintain integrity and safety, even though it will never have to see the sustained loads that inverter does
why do they sell cheap 8ga jumper cables,
because they are seldom used and the use only lasts for "SECONDS"
Again.. it is the context of use and conditions of use that determines what is safe and allowable
6ga wire fused at 60amps.. may allow the inverter to operate safely
but now you look at the performance factor , and will it meet you use
or it will it be shutting off ?
that will be up to you to decide after you try it out on a camping trip