I think its mostly that Austrian economics focuses on the individual and rejects macroeconomics based on aggregate demand. What I really think is going on is not that people really understand Austrian economics and find it logically persuasive so much as they want some reason to ignore Keynesian economics.

However, what I generally understand is happening, or rather is not happening, is called "pushing on a string". No matter how low the rates or availability of loans (not so sure that was true in Japan in the '90s), nothing can get a business to borrow money if they don't think they'll be able to pay it back.

That's exactly right. And that's where a lot of economic theories break down ... because its assumed that firms always maximize profit. If you assume that, firms will always borrow money if money is free (i.e. 0% interest rate), and put the money to use earning >0%.

I think we've seen that's not a great assumption though because firms are not always maximizing profits.