the 737 would not "sit" down.
I find that a little difficult to contemplate unless the pilot gets into a float and deliberately lets the thing sit there rather than putting it onto the ground when necessary. Finesse is fine and we all like a greaser but sometimes it just is not going to work out to our advantage and we need to make it do the right thing.
maybe they did not actuate because of no weight on the wheels for that few critical seconds of skimming along the runway?
which is why you and I will go for the lever to make the boards come up.
Having said that, I recall my one and only "real" greaser on the 722 .. a very uncomfortable and unpleasant feeling not knowing if the tyres were on the ground or a bit above (no shudder or squeak .. it just skimmed onto the runway) .. if the latter, of course, then EVERYONE was going to know very soon thereafter. Mind you, although it was a pure fluke I had no qualms about taking credit for it when the head lady came up after we had parked and wanted to know who had done the thing.
Maybe that is why the max additives are 20 knots?
Going back to the BCARs (and my memory is a tad faded on the detail now) there was a 20kt maximum on Vat. Never found the rational basis for it but a look at the simple dynamics suggests that it was a reasonable balance between final approach comfort and stopping. It should go without saying that the aeroplane has to be put on the ground without any attention to finesse, especially in wet conditions and reverse and brakes are applied vigorously until the stopping state is comfortable.