i think a lot of it is less maintenance needed as plastics and composites dont rust easily. matte black conceals better and less noticable by the sheeple if a slide or barrel sticks out. weight is another huge factor plastics and composites weight less than steel.
plastics and composites are easy to make in molds than machining out recievers from a chunk of steel with a pocket knife
this reduces costs greatly. compare the cost of a good colt 1911 with a similar capacity and sized handgun with similar accuracy and reliabilty made from composites.
all that leads to cheaper and more comfortable carry guns.
we are a in a cost concious time and low priced high quality items sell better than high cost high quality items every day of the week. how it looks is fourth seat to the economic and ease of upkeep and weight to a lot of folks looking for a carry gun.
ccw is driving a LOT of the handgun purchases in the last few years. steel guns are pretty much selling at the same pace they always have as they are mainly status range toys nowadays but the work horses are the plastic parts guns stamped out in assembly lines by robots.
if john browning had access to injection mold technology and high impact composites the 1911 woulda been a polyframed designed.