Every single one I saw wore a hijab. The cleaning staff earned less than the customer facing shop and restaurant staff (who were almost all hijabless).

Istanbul Airport is right next to what used to be Istanbul's Dharavi (a megaslum). Most residents were migrants and ethnic minorities. This was also the neighborhood that Erdogan grew up in, and helped propel him to power.

A major reason he kept winning elections was because he enacted a massive urban housing program that helped convert those slums into normal neighborhoods with public services (and also helped siphon money to AKP aligned construction conglomerates).

And it's people from those backgrounds that were doing the menial work at IST (eg. cleaning staff)