I don't doubt that the platforms count votes properly, but the problem is that many votes are coming from repeatedly-registered people. As in, one person might have 10,000 accounts, all of which upvote something. You can pretty easily automate the process of signing up for accounts, using VPNs and different browser profiles or VMs and also just setting up your browser to delete cookies. You can also use APIs to automate the process, though captcha complicates it. But it would be really easy to have AutoHotKey automate the process of everything aside from the captcha entry. Once you set up all the software, just use Amazon Mechanical Turk or some third world country for outsourcing the labor to get it done quickly and cheaply. Or there are even some dark web markets that sell bulk accounts. There was even one online forum that wasn't on the dark web that was about cheating in Runescape, but there was someone who would sell thousands of Yahoo email accounts at a time (this was a while ago).
Then you get shit like r/LateStageCapitalism getting upvoted to the front page of reddit even though most of the subscribers and votes are fake.
Lots of followers on Twitter and Instagram are also fake. You can tell when someone has a million followers on Twitter but they only get like 20 likes and retweets.
I read a research paper a while ago where the researchers presented people with different music, and they had made up statistics about the number of listeners and downloads. They changed the numbers from one person to the next, and they concluded that people liked the music with the higher numbers.
If you view a Youtube video with 500 views and 2 likes and 5 dislikes, you're not going to like it. When you see something with a million views and 10,000 likes and 72 dislikes, your brain will subconsciously tell you that you're supposed to like it because you think other people have widely accepted it. But those numbers might be fake. It doesn't matter if the site itself doesn't make it up, other users of the site can do that.