Like Blake said, they do not have to declare. Many make the decision to go pro or not after the draft. The really good ones who are predicted to high, may indicate in advance they are going but still have to wait and see how high they go in the draft. College players and high schoolers who want to go but are not sure where they will be drafted just sit back and wait for the draft and then make a decision based on how high they are drafted and how much money they will get. Some high schoolers who will probably be drafted sometimes tell pro scouts that they intend to go to college even if drafted and that can effect where they are drafted, probably slipping a bit in the draft. With some NIL money available for college ball there is more of an enticement to play in college for some of the people. Of course, there are some really good players who still choose to go to college even if they are drafted relatively high because they and their families want the college experience, an education, and development.