I thought it had to do with size/frame. WDE is taller, faster, lighter and able to drop back to LB (like interception in Bama game) and SDE is heavier, and able to get low and move to interior (like Joey Bosa or Diesel). Most top DTs appear to be 6'2"-6'4" and most top DEs appear to be 6'4"-6'5". King, though tall, is a SDE, so more suited to play SDE/DT like Diesel. Robertson, is a tall, lighter WDE, like Cooper and Hall, and even Tuf Borland. Of the two, King seems like more of a need.
Looking at recruits by positions, some are filling up faster. When dominoes fall, recruits need to be ready commit or miss out. We saw this with QBs last year. WDEs and OLB are committing faster than SDEs and DTs. Zero of the top 20 SDEs are committed. Maybe this is why Robertson needed to commit earlier, but Bosa and King can wait.
Interested to see if the dominoes do fall quickly in each position group.