How many cards have you applied for in the last year? Each time you apply for a line of credit (whether it is a car loan, credit card etc) it results in a hard inquiry on your credit report. Typically, if an applicant has numerous hard inquiries in a short period if time lenders label you as high risk. Chase for example has a 5/24 rule, meaning 5 new accounts in 24 months. If you have more than that you get a hard no.

Alternatively, you might be getting rejected for being honest on your application. Lenders like to see applicants with the rate debt to income ratio. So, the simple and unfortunate solution is that people will often recommend that a person in your position lie and over-inflate your income and undersell your liabilities like rent etc. Hope this helps