The market is not that easy to fool. Repurchases are rewarded only if the market believes they are a good use of funds. I, for one, prefer them to dividends. That way, those who want to turn their ownership into cash can do so, while those that don't can increase their relative holdings in the company without investing more cash.
And repurchases DECREASE market cap. So if a company repurchases 5% of its stock, the stock price must go up at least 5% just to market cap equal. If your goal is increased market cap, buying back your stock is a stupid way to achieve it, because you need to overcome the repurchases with larger stock price increases.
I think we both recognize that in the real world, the market doesn't act purely on common sense or logic.
Instead, it reacts emotionally based on how it thinks everyone else will react. It reacts not based on what happened yesterday, but what it thinks will happen tomorrow. The market guesses and builds in those guesses into the price of a stock.
Everyone is trying to get a jump on everyone else. Everyone is trying to stay ahead of the curve. As a result, the market constantly overreacts.
In theory, a stock buyback should have no effect on market cap. In theory, as stock is taken out of circulation, the stock price should adjust to reflect the new EPS, resulting in an identical market cap.
The reality is that the market anticipates those buybacks before they occur.
Thus, today’s stock price (and therefore market cap) is inflated in anticipation of tomorrow’s stock buyback. These anticipated purchases already are built into the stock price.
Think of it this way. Disney’s BOD has authorized the repurchase of an additional 93 million shares (roughly $8B at today’s stock price) while suggesting to the market that even more authorizations will follow.
What happens tomorrow if Disney announces it is cancelling this and all future stock repurchases?
Disney’s stock price will drop. As a result, its market cap will drop even though, on paper, stock repurchase should have no effect on market cap.
Again, how the market actually reacts is very different than how the market should react.
Stock buybacks very much influence market cap.