The fact that this phone is bigger doesn't sit well with this vocal minority, because they want a small smartphone and now see that medium is the only available in stock.
Expectation, expectation, expectation. It's being shattered, that leads to emotions and that leads to comments.
I'm also not too happy about the new SE, if you search my comment history I don't think you see me talking about it, but I'm in the same camp. I think other phones are preposterously big, and the SE is the only normal one.
Alas, the new SE is not normal for me. Going back to a dumber phone is now something I have to consider more seriously. I don't want my pockets to bulge out and I want to handle my phone with one hand without straining it. The old iPhone SE was perfect for that. I have pretty tall hands but with the iPhone 8, it didn't strain but felt clumsy (and I use the device quite often in order to help my grandparents with their iPhone 8).
I hope I gave you some insight into the marketing persona of people who want the old iPhone SE to come back and how that persona is well represented on HN.
See also:
Search on HN Algolia for iPhone SE to see these sentiments repeated. Example: the top comment in the this thread [1].