the same reason that chrome and firefox look like each other way more than they did originally the same reason GNU/Linux distributions like Xandros used to mim

the same reason that chrome and firefox look like each other way more than they did originally the same reason GNU/Linux distributions like Xandros used to mimic Windows XP the same reason Microsoft Windows originally looked a lot like MacOS the same reason MacOS looked a lot like what was going on in PARC before them because users come to your platform with expectations and perceived affordances, and if you can get them to switch others will too ie if your UI isn't defined by lawyers, it will adapt to the psychological models that actually live in the heads of your users if you're developing it properly