Isn't it just the demand is a lot higher than the ps4/x1 launch? I do find that weird since the marketing for ps4 was a lot better than the ps5. I thought the ps5 was sold more than the ps4 at launch as well. Nevermind they had better sales for this launch.
From Venturebeats:
"PlayStation 5 finished 2020 as the No. 2 best-selling console in dollar sales, while PlayStation 4 ranked second in units sold," said Piscatella. "PlayStation 5 set a new dollar sales record for PlayStation hardware through each PlayStation platform's first December at retail."
Microsoft has said that Xbox Series X/S is the best launch in Xbox history.