Large telescopes can directly image the moon, it's just rarely done. This is obvious since an amateur 12" telescope can directly image the sun, with appropriate filters.

Large telescope observing time is valuable, and the instrument package is set up for dimmer objects. Looking at the moon would waste time from higher-priority objects, require filters/reconfiguration of the instrument package, and not show anything beyond a smaller telescope.

In theory the current largest optical interferometers when fully operational will be able to image residual Apollo lunar hardware. In fact a VLTI official said: "we will, if we wanted to, be able to resolve and photograph Apollo debris left on the Moon." http://www.vectorsite.net/tascope_04.html:

I'm not totally sure of that, since current optical interferometry (while impressive) doesn't work well for complex objects at lower temperatures.

The point is we don't need a new generation of telescopes with ever-large apertures to see Apollo lunar hardware. The current baselines of optical interferometers are sufficiently large. Rather additional technical development is needed so these devices work better on complex objects at lower temperatures.