Incentives against selfish miners with 51% power
The minting of bitcoins is constant and a 51% miner can't change the supply of it and cause inflation. Changing the supply can only be done by developers, resulting in a chain split, which wouldn't be called Bitcoin (unless it gains the support of various companies and users)
You can't just mine loads of coins, double spend them and cash out. To spent the reward of a block, its miner has to wait 100 blocks (144 blocks = 1 day) If you're double-spending coins that aren't newly minted, you can do that, but economics says while you own 51% of the network, you would be devoting lots of hashpower (=electricity) and would earn lots of block reward, so you wouldn't want to forget to cash out the block reward. On the other hand, to cash out the block reward, you'll wait 100 blocks, by when the price of bitcoins will drop, and you'll be at a massive loss. In addition, if you have that much of a hashpower you'd want to continue mining for a long time. That means even more loss due to the change in the value of bitcoins.