The bottom line is in the hands of the Forest Supervisor, and it all revolves around how much pressure he's getting from inside, how much pressure from outside, how much money is available in the budget, and how it needs to be spread around to ALL the forest projects and daily operations. Needless to say, daily ops and emergency services needs are fulfilled first, then the remainder is applied to projects. BTW, a "project" is basically anything not in daily ops or emergency service.
A hypothetical example of why some things never seem to happen: you may seem to have plenty of money left over to apply to a given project, say, open new 4x4 trails, but is there also sufficient money to maintain and keep them open for this season, and will there be money to operate next year? Remember, you're not only dealing with the one-time expense of the new project in this year's budget, you're also gonna have to supply money to manage and maintain it for the remainder of this year, and that money's not in this year's ops budget. If there's insufficient additional daily ops money for the new trails in next year's budget, then you can't afford a new trail addition. USFS has to bank money for emergency services (fire ops, etc.), and if that gets depleted during a rough fire season, guess what's first to get cut? That's right, the recreational budget.