I agree with yojoe and Connie:
GetSimple is about keeping it simple, and frankly, something like {pageDate} is just a different syntax of <?php get_page_date(); ?>. And then you would need to specify how to pass parameters, specify conditional tags and more.
PHP is, different than e.g. Java (where you need JSP tags or something similar), designed to be used within HTML pages and using the short syntax of <?=get_page_date()?> there is even less difference.
GetSimple is about keeping it simple, and frankly, something like {pageDate} is just a different syntax of <?php get_page_date(); ?>. And then you would need to specify how to pass parameters, specify conditional tags and more.
PHP is, different than e.g. Java (where you need JSP tags or something similar), designed to be used within HTML pages and using the short syntax of <?=get_page_date()?> there is even less difference.