I have always assumed that crunch removes the need for rulings by the GM, as there are sufficient rules to handle any likely situation. The depth of crunch is representative of the range of situations that may come up, and usually a strong indication of what play will be about.
A follow up question might be: why the aversion to rulings? I think there an be multiple answers.
At some point I think one cause of aversion boils down to: I do not trust the GM to interpret how this would work, and provide a ruling (or even as a GM I do not have confidence I would understand how this might work well enough to provide a ruling). Crunch re-assures all parties in this that the rules will adjudicate this not the GM. It is a lack of confidence and trust in ruling. I think there is a concern there that a poor ruling will invalidate ‘willing suspension of disbelief’ in the world.
Related is the concept that I can use tactics to gain advantage, that I can overcome through ‘smarts.’ Crunch both gives me the options that allow me to find tactics that provide advantage (not always crunch that simulates the world, sometimes crunch that provides options) and the confidence that the rules will support my application of that tactic. Without that, I might be concerned that a ruling will eliminate my tactical thinking.
Personally, I found crunch more attractive when younger and less-experienced (both in gaming, and in the ways of the world) and thus having less confidence in ruling fairly, either as GM, or by a GM with whom I was playing.
As I have got older the trade-off between a loss of immersion due to the handling time of crunch vs confidence in my ability to create a ruling (or of those I play with to) has lessened the appeal of crunch.
However, I know many for whom the idea of tactical mastery is still attractive. The idea that you can ‘beat’ the game.