As far as I know, there are two reasons why college students are easily rejected when applying for credit cards:
Reason one: the age does not meet the requirements.
According to the regulations of banks, applicants for credit cards must be at least 18 years old and have full capacity for civil conduct. The age of most college students does not meet this requirement.
Reason 2: There is no source of income.
To apply for a credit card, the bank must have a stable job and income source in addition to the age limit for the applicant. However, college students have no financial resources, so they can't guarantee timely and full repayment, and they don't meet the application conditions of bank credit cards.
If college students really need to use credit cards, they can ask their parents to apply for supplementary cards.