One of the bigger reasons has to do with the square cube law - as the size of something increases, surface area increases by a factor of 2 but mass increases by a factor of 3, so little fishes have a surface area-to-mass ratio that is quite a bit higher than a larger fish, and they're more susceptible to abrupt changes in temperature.

Kinda like how an ice cube will melt a lot faster than a big slab of ice, the core temperature of some small fish like a goldfish is gonna change more rapidly than the core temperature of a big fish like a trout so they tend to be a lot more finnicky in regard to significant and instantaneous changes to temperature and stuff. A larger fish might shrug off a significant change because it affects them more slowly, but that might be a totally wild an overwhelming experience for a little fish to go through

You can yeet goldfish. Carp are stupid tough. It's the tropical fish we often keep that are kinda wimpy. Also, they're not coming from a super healthy environment (the store) to our tanks.

Maybe 95% survive, but how many are injured in a way that might impact their quality of life?

Since these are being dropped specifically for the purpose of being caught and killed asap, quality of life might not matter.

For your sad little goldfish, please be gentle!

Have a pilots license?

Technique I imagine.