He most likely has insider information that leads him to believe that the stock is going up in the next six months or so. When the price goes up enough, he will sell.
He's been investing for a while now. This is him adding shares as he slowly shifts his net worth more and more into AAPL. You don't make a move like that all at once.
Icahn is no saint and that is clear to everyone. However, he has done nothing wrong with the Apple dealing except providing that hideous picture. He has purchased stock, asked for changes that apple was planning to make anyway and now bought more stock. At some point, he will have enough profit and will dump the stock and make his pretty penny while tanking the stock price. However, as you stated Apple has enough reserves that even a massive sell off by Icahn would be only a temporary dip in stock price. Therefore, I, for one, am not worried about him yet, unless he buys enough to warrant a seat on the board or if he puts out even more hideous picture of himself.
I doubt there'd be any kind of dip in stock price if he sold all his shares. First of all, he probably wouldn't do it all at once, it's unlikely he'd get the price he'd want trying to dump everything in one day. It's been a while since I looked at AAPL's trading volume but it's probably not millions of shares. Remember, in order to sell, you need to have a buyer. He also doesn't own enough shares to make much of a dent in the supply and demand of Apple stock whatever his market actions.
Second, Apple's reserves have nothing to do with anything. Icahn can't just show up at Apple HQ one day with some paper and demand Apple buys it from him. He's going to sell his AAPL shares on the stock exchange to other investors.
Third, I don't think Icahn has enough personal net worth to buy enough shares to warrant a seat on the board, not without AAPL tanking massively first. If that were to happen, I'm sure a smart investor like Icahn would sell his shares before the price dropped that low, or his net worth would also tank.
You're right, though, that Icahn is doing absolutely nothing wrong. I really don't understand why he attracts so much hate on these forums. Anyone can invest in AAPL and anyone can make public statements about what they think Apple should do to manage the company. Heck, people do just that every day on these forums. I'm sure Tim Cook and the board listen to Icahn exactly as much as they listen to all of us

.
So I suppose Carl Icahn was the push for Beats.
That's why the deal hasn't been completed...they needed him to supply the money.
You probably shouldn't comment on stories you don't understand. Sorry to be so blunt, but the level of ignorance of how the stock market works in your post is stunning. I'll give you a hint: Carl Icahn isn't giving any money whatsoever to Apple.