> Can anyone shed some light on the motivation for these frauds?

Money and prestige while it lasts?

> Is there something in particular about the Japanese ecosystem that makes them more common?

Well, the article states the following:

> Michiie Sakamoto, who is leading another investigation at Keio University, into Iwamoto's studies in animals, says it has to do with respect. "In Japan, we don't usually doubt a professor," he says. "We basically believe people. We think we don't need strict rules to watch them carefully." As a result, researchers faking their results may be exposed only after they have racked up many publications.