Why are poisons used less today than they were in the past? What factors influenced this change?

Poisons are less used today because at the time they didn’t have any such thing as knives or guns so they came up with poison using special chemicals and stuff that would kill them but now we can literally just shoot someone in the head and it’s over with but then again you would also have to go to jail for about 25 years in my country poisoning was also used as assassination because a lot of people did not want this one bad person so then they would poison them so that they would die and the land of whatever country that is or rather state I guess you could say would be safe from you don’t let me just give you an example, say there is a bad king and people honestly did not want him because he was terrible and he made horrible decisions well one person came up with a poison or a ton of chemicals mixed together to form something completely toxic and put it in his drink at dinner while he wasn’t looking so that he could die because of the poison which let’s say was going to eat his brain therefore it can also be used as good or bad but now it is used as bad and there are very rare chances of getting poisoned or putting poison in somebody or even finding poison is actually very hard.