I really don't know, I feel as if I've heard it so many times I took it as given. Perhaps it's repeated as it is a simple explanation and the question "why did life move on to the land?" occurs to everybody (second only to "why did we come down from the trees?").

The text in the OP refers to "a massive greening of the planet by non-vascular plants, or primitive ground huggers...roughly 700 million years ago" that oxygenated the atmosphere and allowed more complex animals. "Primitive ground hugger" implies there was an intial partial move to the land before the main immigration. Is there an explanation for the move 700 mya?

Interesting as such investigation is we may not need a definitive cause for the Cambrian Explosion. We have fossils of pre-Cambrian animals and evidence of pre-Cambrian predators. Perhaps the "explosion" was the reaching of a threshold allowing more morphological variety (including those features which are now fossils).

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Yonder is Dubhe seen on Earth tonight as it was in the days of Grover Cleveland's presidency whereas this way is Deneb seen as it was in the lifetime of Muhammed . If one somehow travelled to Deneb at very close to c then whenever you looked back you'd measure Earth as closer to you than the distance you would simultaneously measure between Earth and Dubhe.