Is "looking like Bootstrap" really a problem? Why do webapps/sites really need to look different from one another? As long as they look good, are easy to use a

Is "looking like Bootstrap" really a problem? Why do webapps/sites really need to look different from one another? As long as they look good, are easy to use and have recognizable branding, what is the problem? Say HN used bootstrap with a few small tweaks for colour so it was still identifiably HN. Also your webmail client, hotel booking site & social network. What harm? Isn't familiar look and feel comforting to users? Is there a good reason for the aversion to looking similar or is it just a product of the history of the web, with everyone doing their own thing?