Newer planes do this, but broadly speaking airlines have no desire to give you overhead space. There's an established expectation that they can charge for check

Newer planes do this, but broadly speaking airlines have no desire to give you overhead space. There's an established expectation that they can charge for checked bags, but anything they don't use can be sold as freight space for cargo. Air Canada does this and the money they make from it (~5% of revenue) accounts for a significant portion of their net margin. Plus, the favorite pastime of Canadian airlines seems to be discovering how shoddy they can make their service before there are public riots.