The fun thing is that only the dumb poisoners are the ones that usually get media attention. Exactly because they are dumb. The smart ones usually never get caught.
Consider someone with a medical degree (like myself).
I not only know good and reliable ways to poison someone... I also have quite easy access to the substances. I can obtain some of them without registration. And I also know which substances will not be discovered by the lab when doing the routine post death tests (or ones that are not routinely tested). I am also quite aware which substances are not at all discoverable in my country. Also which ones could be made to look like flu, renal failure, pneumonia etc. Even worse.... If someone like me wants to kill some relative, they can wait for the right time to do it... for example, when the seasonal viruses have done their work (when they want to hide the poison symptoms somewhere amidst the virus symptoms). It will not even raise any suspicion at all...
Don't get me wrong. I have never wanted to poison someone and I can't see this changing.
And my knowledge is not unique by any measure. I am sure every physician does have it, or can obtain it easily by revising some of their college textbooks.