I have several reasons.It is probably me, but I have never been able to .... confidently grasp why running the 3/8 is the better choice.
Less chance of the chain breaking?
Seems to stay sharp longer
Cheaper to buy
Sturdier chassis that stretches less
If damaged there is more cutter to resharpen and even with standard sharpening the chain lasts longer
Everything 50cc and larger takes the same file/ setup on the grinder
Cuts faster... If the wood is small enough that the saw pulls it effectively
I realize some/most of those reasons are very subjective and allot of them are just gut feelings from running saws both ways.... Never took the time to put a stop watch on em and prove them true or false and honestly doubt I ever will.