Why would I want to increase the costs of creatures that I cast?
There's a few ideas that spring to mind. The simple answer is that it's intended specifically as a downside. Most 4/4 creatures that cost {4} (without requiring specific types) have some sort of downside. If it didn't have the downside, it might not get printed.
Even if it's supposed to be a strict downside, though, there can still be unusual cases where you can take advantage of the downside. You could give it to an opponent with Harmless Offering and make them pay the extra costs. I guarantee you that at least one Zedruu the Greathearted player out there is running this. You can cast Etched Oracle for {5} and get a full sunburst. Maybe you want to use Hall of the Bandit Lord to cast a big creature and give it haste, but it has no generic mana in its mana cost. Are these strategies particularly strong or likely to see significant play? Probably not, but there's a lot of players who enjoy finding ways to take advantage of things intended to be downsides.