I believe Visa has around 3 times the credit card market share of MA. In other words, there is not much room to grow competitively.
As a result, Visa's growth has to come mainly from the economy, which is in a slump at best.
When you're a small company, it's easy to defy the economy in terms of growth rate. But not so when you're a big company with a big chunk of the market share. Another example: Google.