Many achievements also have a level requirement, based on Replay Poker Points. (You get those by playing, too.) If you don't have the appropriate level, you may not be able to unlock the achievement -- yet!
For example, if you have an achievement for having 300,000 chips, but haven't met the level requirement for the achievement, it will not be awarded -- even if you have more than enough chips!
There are some hidden achievements without a level requirement that you'll have to discover for yourself. ;)