I think it comes back to the idea of "jack of all trades, master of none." No matter what PhoneGap does, it will never do everything superbly, and sometimes (often, even, I'd say) the trade-off isn't worth it.

There's also probably an ego play, too. I see the "Objective-C isn't that hard. Learn it." argument a lot, but it does have a steep learning curve. For one, it's syntax is confusing if you don't recognize the brackets and messaging. Second, it's a lot closer to C than something like Ruby or Python, so you have to learn about types and memory management.