Why a gadget rather than a handful
A popper changes the timing of colour. Powder thrown by hand disperses over a few metres and a few seconds; a device puts a defined quantity into the air in one instant, at height, on a cue that a hundred people can hit together. That is a different product doing a different job, even though the colour inside is the same corn-starch base.
It also changes who buys. Dry gulal sells through a dealer network to households. Gadgets sell to event organisers, wedding planners and venues, who buy on reliability of firing and on how the colour reads on camera rather than on price per kilo.