Quite simply because browsers are not just used for websites but as an application platform as well. Depending on the design and the requirements of an application modal dialogues and in rare cases even disabling leaving via the back button absolutely make sense.
It might not amount to good UX practices but it's not malware or a dark pattern either.
Besides, if at all possible most browser vendors try to be backward compatible. There are many applications out there that make ample use of pop-up dialogues. There's no need to break those just because they don't provide a stellar UX.
It might not amount to good UX practices but it's not malware or a dark pattern either.
Besides, if at all possible most browser vendors try to be backward compatible. There are many applications out there that make ample use of pop-up dialogues. There's no need to break those just because they don't provide a stellar UX.