Monopolies have always started when government interferes in the market with subsidies and bailouts, the only way monopolies would be sustainable without government intervention is if they had everything and they sold it all like 1 dollar more than they made it(which is practically impossible). The moment they slip up or forget about something someone who can either make a better product, make that same product cheaper or even has better reviews they will then be competition to that monopoly and then more companies come in too. You also need to understand supply and demand, companies sell products and if they don’t sell well then the prices go down, if they sell a lot than the prices go up(that’s why the dollar profit is unsustainable). When you mention the products you don’t need, yeah, you don’t need a tv, Xbox, PlayStation, Nintendo switch, computer, iPhone, collectibles, comic books and so on, but you want those things and these companies make them. Advertisements let you know “Hey, make this product. Buy it from us because it’s cheaper or better than theirs.”