If I was to play a game of word association with you, and I offered the word "clear" (in the context of ultimate), I wouldn't be surprised to get some of the following replies:
The habits that players learn as beginners persist as players move into elite ultimate.
The slow jog back to the stack after not receiving the disc on a cut may be useful in beginner ultimate. But it is a big handicap in elite ultimate.
The offensive player who is clearing is generally not moving fast enough to pull away from their defender. They are not looking at the thrower. They have no body language that says "you can throw the disc to me now, and I want it".
Personally as a defender, I will regularly interfere with the offence when my player decides to "clear". I will float off them and look to get an intercept, or help shut down the cuts of others. Sometimes I will use this as a chance to take a shortcut to where they are heading, and take a rest on the way.
And as a thrower, I like to throw to teammates who think they are "clearing". You may have finished a cut and are jogging away from me, not looking back. But I may still throw to you, and then let you know the disc is coming.
To summarise: always be a receiving option. Cut in, cut out, cut left, cut right or wait in position. Cut slow or fast. But never clear again.