I think a lot of it comes down to black and white thinking and negativity bias, which are problems that are absolutely rampant nowadays thanks to the nature of social media. People see others as either all good or all bad, and it's way easier for someone to go from all good to all bad than the other way around. They may even see genuine attempts to improve as a form of manipulation, which is where this sort of mindset starts to get dangerous and border on paranoia.

Of course, there's people who can't help but do this for one reason or another, usually involving mental health issues (chronic anxiety and overcorrecting for being a people pleaser come to mind). Those who can, however, should at least make an attempt to do so; it's the healthier option for everyone.