Your private mode searches may not be ones that have ads for them, those sites may not use Google's re-marketing offers, the re-marketing may be offered via coo

Your private mode searches may not be ones that have ads for them, those sites may not use Google's re-marketing offers, the re-marketing may be offered via cookies or if they fall into an 'adult' category then you are going to see them in less locations anyway. Despite that a search engine is still able to see what you search in private browsing modes as none of it's protection change, hide or obscure your identity. If you perform a search from your IP address (or any other information that can be fingerprinted from your browser) and then do the same in private browsing mode, Google would know that it is the same user committing both searches.