The reason for using spoilers for roll-control is to do with torsional stiffness in the wings. Ailerons are effective, but they impart a twisting load at a point which is both a long way out spanwise, and a long distance from the centre of wing area chordwise. If the wing isn't stiff then what *actually* happens is the aileron causes the wing to twist in the opposite direction, often to the extent that the change in wing AoA produces a greater roll moment than the aileron - a phenomenon called "aileron reversal". To visualise this think of the aileron acting as a servo tab on the wing TE.
To prevent this situation occuring the wing must be torsionally stiff, and the extra structure to do this is a significant weight penalty in an airliner; one which they'd rather avoid.
One of the earliest solutions to this problem was to move the ailerons inboard to a stiffer part of the wing - as first seen on the F100 super sabre. This approach works for the low aspect ratio wings of fighters, but doesn't provide sufficient roll authority for the high aspect ratio wings of transports. So the alternative is to use spoiler controls which don't impart big torsional stresses. IIRC this was first done by Howards Hughes's team on the sadly abandonned XF-11 project, and then by Northrop on the P-61 black widow. Its use on large aircraft is now almost universal, and the small ailerons which are still fitted are often only there to provide tactile feedback ("feel") for the pilot.