Reports alleged Luke Cage and Iron Fist weren’t all that popular in successive seasons, and it wouldn’t be surprising if Marvel or another platform passed on adding it to its lineup.
Let’s also remember that, while some of these cancellations were suspect, others seemed to have justifiable cause.
A time jump would further disassociate these characters with their one-time Defenders colleagues, and make it more believable from a story standpoint that they wouldn’t inject themselves into each other’s drama.