You have a flag for that: chrome://flags/#autoplay-policy
I think the real answer is: adding such a switch would be very very hard UX-wise. Also imagine what would happen to users that flipped the switch and then never knew how to turn it back off, or whatever. You get the idea.
I do know one thing: Facebook news has become a source of derision due to its quantifiable impact on divisiveness in the US politically. And a scandal erupted on the topic of Russia funding of political ads.
There's a fantastic article on the general topic of Facebook news here: https://medium.com/the-mission/the-enemy-in-our-feeds-e86511...
With all this mess, it's inconceivable that only .01% of people would toggle these settings.
I won't argue against the idea of the UI being too complicated, that sounds absurd to me although I'm no UI designer.
My answer is: The same reason Chrome took away the ability to stop video autoplay. The same reason the Roku apps are crippled so, for example you can't filter search results in the YouTube app or skip Reuters ads in its app or stop Netflix from showing trailers simply by scrolling.
Because the world of media has transitioned from a come-and-find me to one of I'm-coming-at-your-attention. Kind of like TV used to be. Except now we have personalized coming-at-you.
That's why Facebook can't give you settings to fine tune your feed. It would ruin the coming-at-you.
And ad tech can't have that.