Search plus campaigns (also known as
Search Network with Display Select or
SNDS campaigns) only support specific types of criteria: Keyword, Language, Location, LocationGroups, Platform, and Proximity at the campaign level, and Keyword at the ad group level. The reason for this is that
SNDS campaigns are basically
Search only campaigns that also
automatically server your ads on the
Display Network, so any criteria types that are
Display Network-specific (such as Vertical or Placement) are managed automatically for you by AdWords.
This Help Center article goes into more detail on the different campaign types.