From the I&R Institute:
There is no doubt that there will continue to be large sums of money associated with initiative campaigns. But it is important to understand why. The main reason is the growing regulation of the initiative process by state legislators. They have been swayed by the rhetoric that money has corrupted the initiative process – even though there is no academic research to support this viewpoint. Their new regulations are the cause for the growing amount of money in initiative campaigns. More regulation just means that initiative proponents will just spend more money to overcome these hurdles. The loser in this scenario is the average citizen. They do not have the resources to overcome these hurdles and therefore are locked out of the process. If legislators are concerned about wealthy individuals and special interest being the only ones using the process, then they should make the process more accessible to those individuals without access to large sums of money.