There are plenty of arbs around, but the real problem is moving cash - it takes DAYS sometimes. The only realistic way to profit from arbing is to have your cash and bitcoins evenly spread across multiple platforms (which you then have to rebalance as your relative balances change), but even then you need big balances because bank fees eat your cash FAST if you have to move it.

In short, there are opportunities but they are not so easy to take advantage of.