How does the legislative branch hinder the realization of democracy historically and currently?

Well, historically and currently the legislative branch created difficulties for democracy because:
Every 30,000 people in a state = 1 representative who elects the president, as i explained in your last question. So the problem is, the states with bigger population basically have all the power and control the election, pretty much. This is still a problem today (it’s also why the senate was created, so each state gets 2 senators = 2 votes).
Historically, states that had a bunch of slaves would count their slaves as a person just so they could get extra representatives. This is why the Great Compromise was made, so 3/5s of the slave population counted as a person.

high entry costs prevent new producers from entering the market.

explanation:

an oligopoly is a term used to clarify the structure of a particular market, industry, or organization. a market is considered oligopolistic or amazingly focused when it is shared between a few companies.