@Parmandur already covered it, but I think it's worth a little more discussion.
The Basic book (which is the common four races, the core four classes + one sub each, a few backgrounds and enough monsters to run simple modules) was more-or-less a "free-to-play" version of the game. It's not that much less complicated than what the PHB offers, save for a lot less choices and no feats/multi-classing.
When people speak of wanting a Basic/Advanced system similar to the 80's D&D/AD&D split, they effectively asking for two versions of D&D to be made; one that doesn't have all the bells and whistles and one that that has deep customization and rules support. TIMHO, that would be the worst possible setup for WotC as they would either focus support on the Basic version (and ignoring the advanced options) or towards the Advanced one (and thus be incompatible with the basic one). So, if the advanced system uses tactical combat rules but modules are written with simpler "I attack" style rules, the tactical rules are going to feel superfluous and needlessly complex or worse, break what balance the module was trying to accomplish.