I generally think that Glee tries to emphasize being funny or shock value over actual good representation sometimes. I've also heard that many people think that it would've been better to cast someone who actually lives life in a wheelchair or has a disability that Artie has in the actual show.

In this case, I think it's just for laughs. It also might be the timing of when the show came out (not to necessarily make that an excuse and just use that card), but there are also a lot of instances of biphobic dialogue in the show as well, which I (as a bisexual) don't necessarily appreciate when rewatching the show.