Unless I’m wrong, everyone on a HS team gets a trophy in the form of a letter, and there sure are a lot of them on jackets wandering around colleges.
Not in our part of the country.
In football, you have to play in a certain number of quarters in varsity matches.
In cross country, you have to meet a time standard and be a "scorer" (one of the top five finishers for the school) in a certain number of meets.
In wrestling, you you have to earn a certain number of team points (my son's senior year, he wrestled up a weight class for part of the season to allow his backup--a senior who been on the team for four years without earning a letter--a chance to earn one before he graduated).
Other sports have similar requirements that go beyond just making the team.
Letters represent not just participation but actual varsity accomplishments.