* We live in a two party system. China has one party only and others are not allowed. Most countries have multiple polical parties. In the US it comes down to money. It take a huge amount of money to become a political party with access to various jurisdictions and media influence which is more challenging than it sounds because funding is required via donations only and donations are limited by campaign finance laws. A two party system is limiting to us versus them arguments, which are often invalid and absurd.
* People don’t pick presidential candidates. Political parties do. This occurs via primary elections that differ from the general election that really matters. Primaries are scattered so that political parties can experimentally field test their candidates among their primary constituents. These constituents are often not the general voting body comprised of moderate people. This is often how candidates emerge that are generally unpopular and/or incompetent, because it’s a reflection of party tooling opposed to actual voter concerns.
* Even with the support and nomination of a political party candidates need more money to compete. Generally the candidate that raises the most money performs better. Therefore the ingredients to become president are party nomination and fund raising.