Resistive dividers are very unreliable. Older cards may work if they have level detectors for the SPI signals. Slowing the SPI clock may help with these cards. The SD.h wrapper does not allow clock selection but direct use of SdFat does.
Many new cards use edge detectors that require a rise times shorter than can be achieved by a divider. Changing the SPI clock may not work with these cards.
The spec requires a 10 ns rise time in SPI mode.