The most obvious reason you can’t do that is that modern airliners have pressurized fuselages. The other answer would be that they would have to expend a huge

The most obvious reason you can’t do that is that modern airliners have pressurized fuselages. The other answer would be that they would have to expend a huge engineering effort and am mount of money to end up with an aircraft that does what the b-52 already does.