Why are there yearly limits on dental insurance?

Or rather... why aren't they higher? So my dental coverage is 1500 a year. I have at least 3 cavities, but i'm not sure. I'm also having my wisdom teeth removed (they cover 60% and I have to pay 600 still) If I have to pay 600 then they are paying more then that and that pretty much cut my yearly limit in half. Now I have a couple of fillings that i'm having some serious pressure pain. I'm sure there is decay underneith them and one is a very large filling. It's the one that hurts the most. My dentist at the time knew I was paying everything out of pocket so he made it a filling instead of doing a root canal, so i'm afraid that i'll need to get a root canal done at this point which means 1500 dollars worth of work and it'll hardly be covered because my limit is so little. :(
--------------------
They all have a limit on how much they will pay on a yearly basis. Their accountants have figured out the level they need in relation to the premiums they receive, so that the can make a hefty profit.
Source