What the navy needed was in the south. Army leadership was rabidly anti communist and wanted to take after the USSR until their ardor was dampened and credibility reduced by Khalkhin Gol.
Anyway, Japan defeating China was about as likely as was Japan defeating the US. What were they thinking, indeed.
And what the army needed was the navy!
The more tanks, trucks and planes Japan churned out for war in China, the sooner they'd be jonesing for oil. Where's the oil coming from? Without it, how many paperweights do they need?