<?= and <%= both work, why not <?php=

Ok. I have the feeling that I'm going to be making myself a bit unpopular here with my first post, but I mean no offense or disrespect. I'm just trying to understand something. PHP allows <?= if short tags are enabled, or <%= if asp-style tags are enabled, but doesn't allow <?php=. Why? I went so far as to look into the source and as near as I can tell without getting my hands on a C compiler, changing it so that the '{opentag}=' format was equivalent to '{opentag} echo' would take a 2 line patch to one file. I submitted this change as a feature request in the bug system (#16763), and got the incredibly informative and helpful response of "this was discussed to death on php-dev. it's not going to happen." 17 minutes later. I've spent the next 2 days trying to hunt down any mention of it, and having no luck because searching for <?php=, or ?php= turns up no results. So in an effort to understand why and how the decision was made to leave a feature partially implemented, I'm left with no resort except to post here and probably bring down a can of whoop-ass on myself. My appologies to anyone who is sick of this being discussed. That said. Why? - Theo