Twitter causes the problem by limiting the number of people you can follow. For example, people who want to grow their user base follow a lot of people so they

Twitter causes the problem by limiting the number of people you can follow. For example, people who want to grow their user base follow a lot of people so they can getting follows back. You might follow 500 people so you can get 50 of them to follow you. But once you follow 2,000 people you reach Twitter's limit and from there the number you can follow depends on how many people follow you. This is an incentive to buy fake followers, so you can continue to follow the people you actually want.