Unfortunately writing a grant proposal takes a considerable amount of time and effort so many researchers are reluctant to write a proposal that has little or no chance of funding. In theory especially one can make a reasonable determination to their chances of funding so even as the number of theorists grow and the theory budget remains steady, the ratio of funded proposals remains relatively constant.
We will have to see how these rules will apply now that the theory program has been reorganized into a part of the larger Formal and Mathematical Foundations Cluster. Nevertheless if you submit a grant proposal that doesn't get funded you can take solace in the fact that you are helping the community. Doesn't that make you feel better?