A lot of people learning to fly are wanting to be airline pilots, and hence want to adopt more of an airline pilot style to flying an SEP. Big runways and PAPIs also encourage this, as do certain instructors. Equally, the natural urge for caution tends to see a few knots added.
Weekend flyers are often rusty. If you're flying once a month, which turns into once a quarter once weather has played its part, you're not going to be great at xwind landings, and a 10 knot xw having not flown for a few months and only doing ten landings a year is going to be a challenge.