Eric Greenwell wrote:

The gear up landings I'm familiar with almost always
involved some distraction so that the checks were not done,

I did my first and (yet) only gear up landing, luckily on grass, with
300 hours, most of them with retractable gear. I know exactly why this
happened: I was on a cross country in an unknown region and had to
outland on a controlled airport. I knew the airport had a grass and a
concrete runway, but wasn't there before and I wasn't prepared to land
there. The runway couldn't be seen during the approach, but only on
downwind. So I had first to decide that I had to land there, then study
the airport chart, talk to them, enter the controlled airspace, follow
their instructions, navigate in an unknown place with an "invisible"
runway, look out for that runway etc., which all broke my routine. I
always do my checks on a certain point during the approach sequence. But
that sequence was broken and additional workload was introduced, and
that got me. I've reviewed my routine since.

Stefan