In webdev using a framework with HMR having VS Code on one screen and the browser on another is a lot more productive than having to Alt/⌘+tab to see changes.
It is not just when there is a post about a new product or project. More broadly for ANY post here, the top comment and most comments will generally claim the opposite of what the original post presents is true (or some variation of that).
I would say mainly it is just the need for some people to feel good about themselves that they know better, or to try to show that they are smarter than the author of the post (so that again, they can feel better about themselves).
Don't take the comments too seriously. A lot of people think they are smarter than they actually are.
And next time notice, whatever the post is, when you click to view the comments expect the top one to have a contrarian view.
EDIT: As an example, as of right now, this post is the top post on HN. The second top post on HN?
Top Comment:
"Really bad advice! Hard work does not pay"
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Upon further thought, looking at the bright side (less cynical), I guess this does help give a more balanced view of the topic as you get to quickly see both sides of a story. But it's still kind of funny that this consistently happens.
There are many more similar use cases.