Many Facebook users are in the third world / financial situations where data is very expensive and presumably engineers are designing for this. I cannot imagine

Many Facebook users are in the third world / financial situations where data is very expensive and presumably engineers are designing for this. I cannot imagine they're stupid enough to run up these people's bandwidth bills with every single photo they take. Privacy concerns may be ignored, but "the latest Facebook update cost me $500 in data and I make $400/year" will not.