I think it's a combination of many reasons, many of which the article cited, but then from other articles I've read as well.
At least for myself, I've noticed that I have used busy-ness as an excuse to not do something I dislike. A rapidly growing synonym by the way, is I'm "tired."
As for why people stay "busy" beyond the excuse factor, I buy most into the argument about keeping up with the Joneses. We live in a very consumption-driven society and people are always scaling up their "needs" rather than being happy with what they have. Consider the consultant that buys a house upon making manager, and then a bigger house upon making partner. Were any of those upgrades truly necessary for the 2-person couple? No, but they"felt" necessary because that's what we do. We climb ladders and scale up.
I'm less inclined to buy the argument that people stay busy because working provides meaning. It's not that I don't think work provides meaning, it's that I don't think most people find meaning in their work today. Rather, work is the tedium that you experience so that you can climb a ladder and get stuff, and continue the up-and-to-the-right cycle.