They aren't purchased because they are pretty, it's because they are convenient and easy to use. If they have children then they need to keep the laundry detergent away from soap loving kids.
LOL--adults and children are attracted to bright shiny objects. If the pretty colors didn't sell the product, the manufacturers could save a lot of money by omitting the dyes.
Easy and convenient? As though a scoop is a time consuming and difficult task. Please. You aren't fooling anyone but yourself.
When I travel, I use Purex laundry sheets - throw a sheet in the washer and the detergent is released, keep it with the load into the dryer, and the softener is released. And no one is tempted to eat it.