Even sliding-IF receiver suffers from 1st and 2nd image frequencies. It can reduce the image bandwidth, but cannot filter out the image perfectly.
To reject 1st image it needs image filter in the RF section, which is pain to implement.
To reject 2nd image it needs an IF filter between the mixers. The IF changes and the filter's parameters (low and high cut-off frequencies, quality factor) have to change with the IF. It makes difficult to get higher order filtering. Or an other option, to use a fix bandwidth filter on the whole 1st IF range, but the fix bandwidth will let more noise into the system, which decreases the receiver's noise figure.