I think I've figured it out. It's because they don't want to give kids an incentive to look things up during commercial breaks.
Two kids are watching 4kids shitdub #9001
"Hey, Billy, do you know what a riceball is?"
"I don't really know, but my best guess would be, you know, a ball of fucking rice?"
"Well, the commercial break is coming up, so we can just look it up right now."
Because they looked it up, they didn't see the commercial for some shitty, overpriced toy, so they had no incentive to buy it, and, end result is, 4kids loses money. It's economics.