there are actually a number of different cultivars of Papaver somniferum and they are often specially bred to either 1. produce poppy seeds, 2. for producing opiates for medical uses, or 3. producing compounds that are used in things like oxycodone.

Many varieties of the so called "opium poppy" dont produce a significant amount of opium and there are even varieties that don't produce the latex that typically contains the opium at all. The idea that opium poppies are somehow "unsafe" is kind of silly and misinformed.

As for why other varieties havent become the primary source of poppy seeds, it is pretty safe to say that the fact that varieties of the opium poppy can be used to produce opiates is why the opium poppy has remained dominant in commercial cultivation.

Drugs are valuable so it doesnt make sense to choose a crop that can't make as many things as another that is already bountiful.

TL;DR The opium poppy producing opium isn't a bug it's a feature. The reason it is still used is because the fact it can be used to produce opiates makes it more valuable.