Robin has a net that can catch him if anything happens -- he has a network of people (friends of his, of his parents, of his extended family) whom he can call upon.
Guy doesn't have that. He only has the Sheriff and Marian -- and thus far, Guy is little* more than a tool to both of them.
* = I say "little" rather than "nothing" because there's a glimmer of hope where Marian is concerned.
Long story short, Robin can do things that Guy can't, in no small part owing to the fact that Robin has people as the saying goes.