Because you have to blindly trust a centralized authority to administer the medicine. I have multiple friends who joined the military who were required to take mystery injections and they weren't even allowed to ask what it was.
There is no more trust left to give. The establishment has proven time and time again that they don't give a shit about the people they have authority over. That's why.
You lived in a time when you could actually trust that sinister things weren't always going on in the background. That time has passed.