Best of luck to him! Because professional running pays so little relative to 'big league sports,' it makes sense to treat it like a normal job and not stay till the bitter end -- whereas even the worst player in the MLB making the league minimum is making a lot more than a first year corporate lawyer or something like that. For a not-quite-A-lister like Sam, it makes sense to finally pick a career (or at least a good stepping stone to one).
If Sam is not an A-lister then who is? I would argue that he is currently one of the top 5 US distance runners.
Here are his PR's: