It's almost like we don't value it for itself, but what it's worth in "real" money.
I think we keep converting it to dollars because that is the only way we know its value or how much it is worth, and not just because we do not value Bitcoins for itself. Just like all other currencies, I think it needs to be converted to other major currencies for comparison and contrast to know how much our currencies are worth in the world market and to assess how well or badly it is currently doing.
Perhaps people have diffirent reasons but mostly they wants to increase their wealth so they converting bitcoin back to dollars and then they buy back the bitcoin in a low percentage of price so can wait another good price hike to sell it again to make it a good profit.