I think I saw a stat on drop goal success rates, and the article stated that it was quite a low percentage rate - but I can't remember what it was, and I can't find the article.
With the analysis in the game these days, if they're deemed low percentage chances, teams just won't go for them.
What annoys me most though is when teams get a penalty advantage in front of the posts, and then go for a drop goal.
If they're getting an almost guaranteed 3 points anyway from the penalty advantage, it makes no sense to me to take a risk at 3 points from a drop goal.
That's when teams should be doing something risky to try to unlock the defence.