Sort by oldest. They had two papers in 2017 and three in 2018. It was only in 2019 that they started opening up more, but you can't change decades of culture quickly. The AI researchers I know (and I know a lot, having been VPE at multiple AI companies) would rather work with groups that are more open.

They did start this but they were a few years late to the game, so they're probably having to play catch up.

Also they still have a streak of secrecy so I wonder if any researchers are skittish thinking that Apple might just arbitrarily stop them from publishing certain papers?