Why would dr order an mri with and without contrast all at once? wouldn't one mri with contrast be sufficient ?

No reason. Yes.: All MRI scans with contrast have sequences obtained before contrast administration. So, in fact are without and with contrast. If a patient es allergic to contrast or has poor kidney function, contrast is contraindicated and only non-contrast MRI is performed.

MRI unlocked: As a routine when obtaining an MRI with contrast we obtain contrast images prior to contrast administration so it can be determined what is enhancing. Routine contrast exams are always ordered without and with contrast. Noncontrast exams are ordered non contrast, and only supplemental followup to an incomplete exam would only be ordered with contrast.