OLEDs can display true black whereas standard LCDs cannot. If the black regions are compressed and blacks become something close to black, but not quite, it looks bad on an OLED as that region is illuminated. Netflix appears to compress blacks very heavily, so you end up with large rectangles of slightly different dark shades, none of which are really black.

I'm not an expert on panel technology, but I think because LCDs have a backlight, the issue isn't as pronounced there. It just kinda washes out.

I've also seen this issue on regular LCD TVs with HD streams. It can get really pronounced in scenes with slow camera movement where a static dark background turns into a blocky, jumpy mess of compression artifacts.

I want to trust that the codecs know that it's hard to see dark, so I wonder if the displays are being calibrated incorrectly, maybe to pump up the brightness for the showroom.

Fortunately, Netflix is the only service exhibiting this issue. Blu-rays look great in 1080p and UHD. Other streaming services look good as well. I've also tried Netflix on multiple devices connected to the TV. In all cases, the Netflix HD stream is distractingly blocky during dark scenes.

My best guess is their choice of codec and compression settings predate OLED availability and they don't want to re-encode and just expect people to upgrade to their 4K plan. I've never had their 4K plan, so I can't say whether that truly addresses the problem.