I suppose it depends where you are, up where I am the simple explanation is that every summer starting with 2007 to the present day has been terrible with none of the prolonged heatwaves that are required for proper storms. 2006 was the last year when I saw decent thunderstorms here and there was a good few of them, but that year was scorching hot from May to October with only a few cool periods.
Everyone flocks to the convective discussion threads whenever we get these mini heatwaves but the stone cold truth is they simply aren't good enough for proper thunderstorms as there isn't time for sufficient energy to build up except in rare situations where a plume is involved, you aren't going to get tropical thunderstorms out of just one week of hot weather any more than you are going to get 400 bhp from a 1.2 corsa engine.
What we need is a prolonged spell of very hot weather, say a month to six weeks, then for it to break down with a cold front passing through. This would give us a widespread outbreak of powerful storms.