are there other technical or regulatory explanations?
A few points to add to the excellent answers already given:
Different aircraft models vary widely insofar as getting smooth landings. If you fly a lot, keep track of the aircraft type and what kind of landing you experience. Over time and many landings, you may see a difference.
In my own experience as a pilot, I found the Boeing 727-100 to be the hardest aircraft in which to get consistently good landings. Actually, I was never able to get consistently good landings in the 727. A string of, say, four landings in a row that could reasonably be described as "smooth" was rare. The joke among our pilots was that for the last six vertical feet before touchdown, it was the airplane, not the pilot, that was deciding what kind of landing it would be.
On the other hand, the easiest aircraft to get smooth landings in for me was the Boeing 747-100/200. You rarely got a landing that wouldn't be described as a good landing. Landings in which the first indication that you were down was the deployment of the speed brakes were not uncommon. When the mains were on, the speed brake handle in the cockpit would very noisily come out of its detent and travel all the way aft.
The pilot's landing currency also plays a roll. A 747 pilot's day is one leg, one landing. If the pilots are trading legs, you're only going to get a landing every three days or so, maybe less. Commuter pilots on the other hand can get multiple landings every flying day. We tend to be better at doing that which we do often.
It doesn't often occur, but an aircraft configuration different than that which a pilot is used to can also affect the quality of the landing. For example, when they load 747-100/200/400 freighters they aim for a zero fuel weight c.g. of 26.6% MAC. One day due to the unique load we were carrying, the c.g. was up against the forward limits, 13% for both the zero fuel and landing c.g.s. The difference between 13% and 26.6% translates to a little over 44 inches. That meant that once the mains were down, the nose would want to fall through much more quickly than normal. I had forgotten about the forward c.g. and failed to use the necessary up elevator. The nose gear came down on the runway really hard, so hard I embarrassingly asked the flight engineer (an A&P) to inspect it.