For a big corporation it is not important to succeed in most acquisition. The real risk, is that some startup eats your current business model and you didn't buy it when you could still afford it. If most acquisitions "fail" that is ok, you still sit on a ton of money.

In other words, probability is more or less irrelevant, because if you fail it means a small loss which does not risk the company's future, on the other hand, if you don't acquire, and the small business succeeds big time, then that is a big loss, and may eventually kill you.