That payback agreement is called royalties and production tax. There is risk in everything in business. Before the credits the risk was too high for operator investment, therefore we as Alaskans were seeing resources go undeveloped. The state took on economic risk to motivate development thereby increasing the potential of favorable payback as resources were developed. It's undeniable that developed resources present a greater likelihood of economic benefit to the state than undeveloped resources.

The state did not want to do a front end spending plan to spur resource development, so they rolled it into the tax side (a common gov tactic, see: Affordable Care Act).