The Stranger Things intro scene is CGI. Artists were consulted who originally created similar titles in the 80s with practical effects to see how they could do it too. The old-school artists said to just do it in CGI because that’s what they would have done.
People don’t hate CGI - they hate bad CGI. It’s hard to explain, but you know it when you see it.
Bad practical effects do exist, but even when bad they don’t look “unnatural”.
I recall Amazon’s Lord of the Rings title sequence [1] received some criticism for looking fake, even though they filmed it practically [2]. I’d guess it was due to folks assuming title sequences are CGI, combined with the fact that few people really know what poured liquid metal is supposed to look like.
[1] https://www.youtube.com/watch?v=HV-dDyYgwkc
[2] https://www.youtube.com/watch?v=sZEpWvQFXqQ
There's a similar problem with gunshots and explosions - we want what movies have given us which is not what they actually act/sound like - so much so that live recordings of actual gunfire/explosions is often deemed "fake".
This is also the American/bald eagle problem. When people hear their actual cries, they’re often confused.
https://www.youtube.com/watch?v=PQ2uMauyBow vs https://www.youtube.com/watch?v=z8SdqOT_no0
Speaking of "Bad CGI", the making of the HBO Intro: https://www.youtube.com/watch?v=agS6ZXBrcng