My local where I discovered them has a girl who DOES care for them every day and the aquarium lead also is feeding them.
The problem with shipping fry is simple: the earlier in life you starve ANYTHING the worse off, slower growing and shorter lived it will be.
These tiny things are just at the stage where their growth becomes driven by hormones and if they aren't fed real
food they will begin consuming their own calcium and protein sources. Someplace back in the records you can find where I tried to recover a male I named Flop. He didn't make it because there wasn't enough left of him to successfully digest food.
In my local store's case, I'm fairly certain the care they're given is enough that if the "baby betta" is given a warm clean safe tank with proper maintenance it will survive for much of its life expectancy. The problem with schemes like this is they're simply corner cuts and this one reminds me of a cartoon where the ice cream truck was handing out pints of heavy cream and tongue depressors. There are just some things very few people are prepared to do at home.