It's not. I've heard three very distinct reasons why it was delayed, before the pandemic, and they're not neccessarily mutually exclusive.
- The initial series premise was the Emperor and a team of familiar faces go back to the 1990s for whatever plot device. This concept was then spun out into its own potential series, with a producer from Halt and Catch Fire now involved. So the series was delayed to plan a new storyline.
- Michelle Yeoh signed on to film a small project she's producing, a bigger Marvel movie, and the Avatar sequels, plus the sequels to Crazy Rich Asians. The timing meant the series needed to be delayed to 2021. Those films are good publicity for the series, so no issues from the higher ups.
- Discovery wants the Emperor in all of Season 4 and 5.
So let's see.