The step from PPL to full IR is just too big for the majority of recreational pilots.
Do you mean the step in skills, or the step in training time and costs?
I think the latter is more of a problem than the former; but the biggest issue is currency. For many pilots it is expensive/impractical to maintain even FAA IR levels of currency (one IAP per month). I am in the lucky situation of being based at an airfield with an ILS and even I struggle to fit in the one approach per month (which I aim for as an IMCR holder as this seems a sensible approach - with a personal minimum of 500ft precision/600ft non-precision but on the understanding this is voluntary and not mandatory - an argument for another time :-) )
Tim