Why magento not use smarty template engine for templating purpose
Smarty is fast, template file look preety, and desiger can easily write html tag(modfiy tag).
In phtml if we want to write code of php then we have start form php tag that is very annoyed.
Magento doesn't use smarty from the start so it will most likely not use it in the foreseeable future.
That's said, Magento 2 will also add support for Twig which you can learn more here: http://twig.sensiolabs.org/