James, sorry for the slow reply. The key point in the discussion is that senatorial families were restricted from various forms of commercial activity in the late Republic. This included contracts to provide the Roman state with various goods and provisions. Since they were shut out, non-senatorial families (members of the equites class) moved into the gap, and many became very wealthy. This was what I meant in that portion of the lecture you’re asking about.
I hope this helps.
