> Isn’t it only recently that the conspiracists have gained so much ground?
It's always existed to some extent but the anti-vaxxers' attempts to promote the idea that vaccines cause autism really escalated things in the years around 2010, and covid gave them another major opportunity to raise fears and conspiracies.
There's also recently been an increasing (and often well deserved) lack of trust in science and medicine. These professions have refused to police themselves and they've allowed absolute junk to get published in "peer reviewed" journals, allowed corporations to pay for research concluding whatever they want to see in a press release, and they let ineffective and harmful medications be pushed onto the public by doctors who took kickbacks and bribes. The extreme lack of oversight and accountability at every level has made it increasingly difficult for people to trust these institutions and that's made people fearful and incentivized them to try to research things themselves to find out what's safe or best.
This has opened the door for a handful of charlatans and scam artists who seek to profit off of that fear through social media by deliberately misleading people who often don't have the education to know better, which isn't to say that they're not smart or even that they're generally uneducated. It's just that our education system is a joke. One of our two political parties opposes teaching critical thinking skills and casts doubt on even well established science and higher education in general. The average American reads at a 6th or 7th grade level and research papers aren't written for them (some have argued this too is often for petty and self-serving reasons)
Most of the antivaxxers are just people trying to do their best for themselves and their loved ones in an environment where they don't know what's trustworthy. Mixed in with them though are nutjobs and the people who know the movement is bullshit, but want to keep making money and fame off of the scam.
Meanwhile, little has been done to increase trust in science and medicine because of regulatory capture and all the money to be made pushing lies and bad medicine. An increase in antivaxxers and conspiracists is basically inevitable unless this changes.