I guess he's entitled to do whatever he feels is right, for him and his pocket, or maybe him and his dreams of knee research. I'm pretty sure he's plenty comfortable in life, as far as personal wealth goes.
I'll bet if you asked him why he might go private, he'd probably say the whole process of maintaining a quality status on Nasdaq, with reporting every single penny involved, form 4 restrictions and scrutiny, people shorting the crap out of the stock, constant compliance and filings, etc, etc, etc.....
Maybe he's just tired of all the hassles of remaining listed.
That 40 dollar peak way back when, I think, was a momentary fluke. A payout at 19.50 a share, would satisfy most IMO.