An algorithm decides what content a person sees on any given platform. This means that a platform can decide how many people are able to see your content. Since nobody really knows how each algorithm works, marketers are left trying their hardest to create the best content they can in hopes of ranking higher.
There are two kinds of reach: paid and organic. Marketers can use paid campaigns to try and get their content seen. Though this may work, ideally you would want to save your money and reach potential customers without having to pay for it. This is why marketers are constantly trying to write engaging content and trying to figure out each platforms’ algorithms. They are trying to reach clients organically.