Let's not kid ourselves here. Marriott, and any other loyalty program operator, makes decisions around elite tier benefits based on data. Lots and lots of it.
They will continuously analyze the behavior and spend of their program population by tier level, look for revenue lifts and drops by segment , and compare this to benefits usage and cost in collaboration with properties.
They will also continously benchmark against their major competitors and buy lots of 3rd party data to detect any shifts in market share - again, on a very segmented basis.
Based on all of the above, the program will be calibrated to maximize contribution and minimize cost. That's it.