Since the percentage for each reward is fixed, there will be a balance. That is, at some point, rewards for staking is lower than rewards for curation. And another variable to be considered is marginal costs and benefits of users. Some users more weigh psychological satisfaction over financial profits, and hence less care about smaller curation rewards. Some others do not want to spend time and effort for curation, and may be more willing to remain in staking even the reward is smaller.
The points from 2 are based on the point 1, which I rebut above.