Kevin Garnett's autograph seems to have "regressed" over the years...
(a) Illegible, but at least look nice enough
(b) Then start getting "simplified"
As for Kobe, his full autograph is actually also the first version of his certified autograph (see the cards that he signed for companies before entering NBA). Once he entered NBA, he signed his first name only for a long time before switching back to the full-name one again.
I heard that currently when Kobe signs autographs for fans in person, he even just signs "KB".