Securing low interest loans to buy assets that appreciate in value with relatively low out of pocket money is basically investing on margin. The ROI on just the downpayment portion is many times more than if you'd lock up all the money by paying the entire amount. A game that only the rich can play.

I doubt it's all tied up, as his last recorded sale (in 2013) http://www.secform4.com/insider-trading/1548760.htm must have left him with quite a bit of cash. So motives are not perfectly clear.

On a macro level, the government penalizes selling of assets at 23.8% (current long-term capital gains + ACA surcharge) and on the other hand encourages borrowing by keeping the rates low and allowing the interest portion to be deducted as an investment expense, so what's a rational person to do?

You borrow against your stock, of course, so you don't have to realise the capital gain yet get access to the cash. If you're worried about downside protection, you can always buy a put option for the stock you pledged at its current value.

Many publicly traded companies prohibit their employees from buying puts or selling calls on their stock, as it misaligns incentives, similarly to how shorting the stock causes you to benefit from a decline in price.