And skill level. It's not an absolute that true expert level skiers need or seek big, heavy and stiff, even for on-piste.
I skied with one such rarity in Chamonix. A certified French mountain guide and ex ski racer working his way up to the word cup ( before an injury ended his racing days) . This guy was 6' 2''ish and fit but not necessarily a light weight. Born and raised in Chamonix. He skied on 175 cm ZAGs that were 72mm waist, and with dynafit bindings his skis weighed almost nothing compared to our skis ( if you know ZAGs, they are extremely light, even for their class ). And of course he was on AT boots. He guides all year and does randonee races in his spare time. He told us he skis those skis everywhere, everyday. He was our guide for a week. We had a mix of every type of condition, from ice and icy bumps lower on piste to thigh deep pow high and off piste. The pow was at times light, and then at times thick, heavy and crusty. We were a group of Americans who were on longer, wider, and stiffer big mountain skies, we were all solid skiers. He skied everything on those light skinny short skis with the aplomb you'd expect from someone born on skis and who skis almost every day of the year in every condition imaginable. He relished in "out skiing" us ( and of course he would out skis us ) in his light touring set up; so much so that often when we took our skis off he'd pass his light weight skis around for us to feel how light they were in comparison to ours, and then he'd chuckle at us and make an amusing comment about how over geared we were ( it was all in good fun). He showed us some of the lines he skis that he needs to repel down to to begin skiing and then repel out of - sick; we didn't ski those with him.
Is he an outlier compared to the typical expert weekend warrior, sure. He's even an outlier to the typical expert professional skier skiing big Alaska lines in extreme ski movies. But, the point is, we almost always attribute big, heavy, stiff skis with experts. The ski ranking and rating review system, to a ski, will place the burliest skis at the expert. Expert skiing is not always about muscling burly skis into submission. There are those that possess expert level talent that prefer a lighter softer ski.