With the Moon there's at least the argument that any contamination likely couldn't travel too far due to the lack of wind. So any contamination there would just

With the Moon there's at least the argument that any contamination likely couldn't travel too far due to the lack of wind. So any contamination there would just be around the landing site, only going as far as the depressurization might've allowed it to go. Plus since the Moon is exposed to completely unshielded solar radiation, any unsheltered contamination will probably have broken down. Mars on the other hand has wind, is slightly more protected by the atmosphere and increased distance from the Sun and around the equator summers are actually at decent temperatures for life.