spicemace said in forum #442685:
Where did the name 'degicat' appear from and why is it the main name on this artist instead of their current name?
If you look at the artist entry's history, you'll find your answer - when the entry was made in 2018, that's the name the artist used, デジキャット, with their Pixiv stacc being dicat902 and Twitter handle being degicat, the basis for the tag name. By 2020, however, they had transitioned to their current name of みゅるめーく, with the Twitter handle being first changed to myurumeku and then to myurumake which it still is today. The fact that the Twitter intent link listed in their artist entry remained unchanged for the past eight years indicates that all they've done is change their Twitter handle, not their Twitter account, pointing to continuity from degicat to myurumake.
As for your second question, that's obviously because no one has bothered to change it to their current name.