Well , in otb chess its against the rules and you can call the TD over and have him stop it . In online its distracting and if you respond in any way it costs you time on the clock . It would be easy for any competent programmer to write code to put a stop to this particular annoyance if they so desired . Obviously they don't so desire .
Yes, I agree that if it got out of hand, you could fetch the TD. But I've never met an annoying opponent that I couldn't ignore by using earplugs and a baseball cap pulled low (I would rather be friendly if they behave). But I don't understand how it's an issue online. You don't have to respond at all to draw offers on chess.com, just make your next move. And of course if the opponent tries to distract you by chatting, mute the chat.
@NM Reb: I never saw the "offer" button becoming "claim". You simply must know if the repetition happened and then offer the draw, if you are correct then it's automatically a draw (like in OTB). That's why I asked this kid to post his game, I suspect it wasn't a system failure.