Response
The original post raised several questions.
If you posit surprise, then surprise occurs.
During WWII, several low level sabatours were landed in this country and promptly rounded up and executed. They did not blend in. They did not all speak the language very well. They became disoriented and fatigued.
Now, 10,000 guys land from one ship. How far can they walk in one day? Do they have any supplies or is this supposed to be one of those "living off the land fantasies?" Do they sleep? Do they get tired? Do they speak English? You haven't stated any "goals" of the 10,000.
Can 10,000 inflict damage? Of course! Can they burn down a city? Of course! What is the point?
During the Vietnam War, I often wondered why there wasn't sabatoge commited in this country on behalf of the North Vietnamese. Conversely, imagine 10,000 people who don't speak English rushing around in San Pedro Ca.
During the last Presidential election, one of the candidates came up with a solution to Afghanistan. He wanted to double SF. Well it cost $1M a year in 2002 to field one Seal. And the total no. of SF and alphabet soup people is about 35,000. So, would a total of 70,000 troops sent to a country with no roads win? Would you spend another 350 billion a year? Would you understand that it takes about 12 years to develop an SF guy? No. You just fantasize. What would happen to 70,000 SF put into Afghanistan with no supply? Oh, well, 10,000 undisciplined and ill trained Somalis are supposed to do better?