He was an actor, so it was all about how he looked on screen, the extremely lean look and speed gave him a unique look and it obviously worked.
As others as mentioned, he could've been heavier and was, but this look worked for the movies.
i remember my "wake up call"
it was in the summer of 2010
a fat girl at work said "you are going to be bald in the future, you know how i can tell? because the shape of ur hairline"
i was completely stunned baffled and shocked
in denial instantly
said to a colleague, "get a load of what this chich just said, she said i'm going bald because of my hairshape"
i was hoping for reassurance
but he said
"what, you mean the mickey mouse shape?"
my world was shattered