Forbes does proactive research on plenty of people who would never grant them an interview or tell them anything.
But think about the poverty of this argument:
Begin by asserting, with zero proof, that there must be 300 families that control the world.
Someone points out that those who track such things for a living have data that completely contradicts that assumption.
You can respond rationally by saying: "I have different data that supports my thesis, let me show you."
Or you can continue along the path of unsubstantiated assumption by saying: "Well your data is collected by people who are beholden to the magical 300. They must be liars" or "The magical 300 would never let anyone know who they are or that they even exist. The people who collected your data are fools who have been tricked."
At this point, the magical 300 becomes an article of religious belief - and it becomes useless to try to discuss it rationally.
Which is the essence of conspiracy theory - the belief can always be preserved if you add just another far-fetched twist to it.

I’m the 301st wealthiest guy, and I’m like totally snubbed for not being included.
(*pout*)
“Which is the essence of conspiracy theory - the belief can always be preserved if you add just another far-fetched twist to it. “
Ding ding ding, we have winner!