These loans come with a relatively high APR. The interest rates on loans with no guarantor depend on the applicant's eligibility. If you have a low credit score, you'll be presented with higher interest rates, as the lender takes a higher risk by lending to you. This makes loans without a guarantor more expensive compared to other cash advances.
The reason behind this is simple—an applicant with a bad credit history is a risk for the lender. If you have a co-signer on loan, the lender knows that the loan will be paid, even if you're not the one to do it. Since you're taking out a payday loan without a guarantor or any other type of collateral, the next logical step for the lender is to compensate with a high interest rate.