I thought this would be easy to answer, turns out there are several pages of discussions on belt types in the book “Small Arms”, DF Allsop & M A Toomey, Brassey’s Land Warfare, 1999.
Fabric belts stretch, rot. Metal belts are more expensive, weigh more.
There are advantages and disadvantages to the continuous metal belt and the disintegrating link metal belt. Maybe the greatest advantage of the disintegrating metal belt is its flexibility.
Metal belts are stiff and soldiers will pour oil on the belts to make them more flexible. This is anathema to the US Army as the memory of the 1921 tin can ammo coverup still rules the day. Hatcher and Townsend Whelen spent the rest of their lives claiming the pressure problems with the 1921 Tin can ammunition were not due to the bore obstruction created by the tin jacket cold welding to the brass case neck , but rather a practice that the shooters were doing. Shooters were dipping their bullets in grease to reduce bullet fouling. The Army created a coverup, General Hatcher and Col Whelen the spokesmen, which blame shifted the entire problem onto the shooters and their grease pots.
In Sept 2008 USATCES put out a bulletin “Don’t Lube your Ammo!” in which they warned about the “evils” of oils and greases on ammunition.
I contacted the guys at USATCES, and they are great guys who are trying to do the right thing, asked for data, and found they did not have any. I did learn from one Safety Expert who had been deployed a number of times that Soldiers will pour oil on these metal belts to make them more pliable. I also suspect that oil may make it easier for the round to be pulled from the belt making jams less likely. I later contacted the USATCES author who actually went above and beyond the call and he asked a number of organizations for data to back up the bolt thrust warnings in his article. He got nothing other than unsubstantiated claims. The author later wrote “If that's true, then I'm guilty of spreading gossip!”