Just as an FYI
USMC is not regular infantry. They consider themselves elite light infantry and was one of reasons they historically resisted joining SOCOM.
Though within the MC they have elite with elite units - MARSOC raiders and Radio and Force Recon Marine
Ignore all the hullaboo that they make. A US Marine is no different from an Army soldier except they focus on the amphibious stuff a lot more.
Marines try to compare themselves to US Army Rangers (the only true "elite" light infantry) but it's laughable. Their training duration and everything else is identical to that of an infantry soldier (barring traditions and culture).
Raiders and Force Recon are SOFs, yes, but Marines have created this myth around themselves as being some elite force.
They're amphibious infantry, plain and simple.
As for their resistance of joining SOCOM, a regular Marine has no business in it. Force Recon wasn't spared by the corps to join it and that's all.
No one ever prodded the regular Marines to join SOCOM.
It's nigh impossible to create and maintain some 2 lakhs elite soldiers with the budget allocated to the Corps.