@ dpandslemmen, You did miss it. The article says:
According to Chatterjee, his findings can be explained by two often-cited theories of behavior – “motivated reasoning” and “fuzzy-trace theory.” Motivated reasoning implies that individuals find spending more enjoyable than saving and are motivated to search for reasons to justify spending. In such situations, vagueness enables them to distort available information to follow desirable spending motives. And having multiple accounts provides that vagueness.
“Basically, people look for an excuse to spend, and vague information facilitates this,” Chatterjee said. “And having multiple accounts provides just enough vagueness to do the trick.”
In other words, Chaterjee says that some people want to fool themselves into spending vs. saving, and having multiple accounts complicates matters enough to justify them doing what they already wanted to do anyway. They might reason that it's all right to spend what's in one account because they have three other saving accounts. I think that most regular readers of this blog are not that naive.