I can't write a whole essay, but I can definitely give you some main points for it.
Back in the day, when TV's still had knobs and antennas, there weren't many channels to choose from (obviously). Even when each American household had a TV in 1965, there were still only three channels to choose from, CBS, NBC, and ABC. Any TV shows or news broadcasts were primarily on those stations. However, by 1970, that number had skyrocketed to over 700 UHF and VHF channels, and advertisers had jumped on the opportunity to market to Americans through it.
The need for niche networks arose from a need from consumers to easily find things they gravitate towards, such as soap operas, science shows, cooking shows, etc. It also arose because advertisers wanted to market via the niche method. Instead of marketing to a whole bunch of people and hoping the ones they really want to target receive the message, they go right to the source with niche TV, tailoring their advertisements to increase their consumer awareness and potential sales.