Couple of other things with this:
1) Some owners (pension funds especially) are not buying shares to gain profits from increased prices, they are buying shares to get an income from dividends. They will usually be doing this in something like a FTSE 100 share index which means that the only time they look to sell shares is when a company drops off the bottom of the top 100 companies, and the only time they buy shares is when a company enters the top 100 companies. What this means is that they will always buy/sell at the lowest price in that bracket. As the price of the stock market rises over long term periods, they are anticipating always being able to sell shares at about the same or a slightly higher price than they bought them for - essentially they are just swapping shares from one company to another. I assume that their rental agreement allows them to demand the return of shares that they want to sell, I know this is possible.
Short sellers may well be looking at short term price changes and trying to do whatever the short selling version of "buy the dip" is. They think the price is going to fall in the short term - doesn't mean they think the company will go bust or the shares will become worthless. They just see something which makes them think there'll be a price drop in the near future. They might even think that long term the price will rise but it doesn't matter because they are in it for the short term.
2) The owner might disagree with the short seller and think the share price is going to rise, not fall. In this case renting out the shares is just pure profit from them. Perhaps they get it right, perhaps they get it wrong. In any case, if they are wrong they'd be losing money on the sale of the shares anyway, this way they get to hedge their bet and earn some money if the share price collapses.