Because he DOES interfere with Buffy's sacred calling. The episode opens with Buffy trying to, you know, do her job, and having to babysit "her Cub Scout." (NB: All Riley insults in this post come courtesy of Spike, who is very good at it.)
|"'Sup. You're cool with me patrolling, right?"|
Whereas Giles is becoming a capitalist and Xander is becoming an artisanal carpenter, Riley has yet to find a substitute to replace the Initiative. And naturally, that's entirely Buffy's fault and responsibility to fix. (All sarcasm in this post comes courtesy of me, who might not be good at it, but certainly relies upon it as a primary mode of critical inquiry.)
Because he DOESN'T let Buffy and Giles have their moment. Giles (and Xander) transformed the back of the Magic Box into a pretty rad training space. Which it is difficult for Buffy to immediately appreciate, BECAUSE RILEY TACKLES HER LIKE A GIGANTIC TOOL.
|Typical performance from "the enormous hall monitor."|
This is merely the latest, Initiative-enhanced-but-not-created, evidence that Riley cannot handle Buffy being stronger than him physically. Yes, it's just that demeaning.
Because he DOES play pick-up basketball in jeans.
Because he DOESN'T want to be "Joe Normal." Buffy learns from Graham
|Still looking fly, G.|
that unless Riley has emergency surgery he could die from blah blah blah. He resists until the last second because he doesn't think Buffy will love him if he isn't a superhero. Little does he realize that it's much less his lack of super-strength and much more his crippling insecurity that turns a girl off.
Because he DOESN'T have shirtless prophetic dreams. Whilst Riley is acting out, Spike teams up with Harmony to engage in an ill-fated scheme to get the chip removed from his head. It's another soap-opera twist in this episode that seems to be full of them, but what matters is that his obsession with the Slayer is revealed through a dream to be a transferred and re-channeled expression of his . . . LOVE FOR HER.
As an aside, for a show that seems pretty deeply suspicious of doctors, including psychiatrists, it sure seems to believe in the efficacy of dream-language to reveal deep and abiding truths about its characters and plot.