That may have something to do with senior commanders lack of enthusiasm for trying to use them.
I think we do not have one vehicle that does everything we want it to do while we fight the Three Block War. There are missions M113A1's could do fairly well, like roadblocks and mechanized patrol of known hostile neighborhoods, but other missions such as convoy escort and presence patrols in more or less friendly neighborhoods M113A1's aren't the best vehicle for the job.
We need vehicles to fight the convoy battles.
We need vehicles to patrol more or less friendly neighborhoods, maintain presence, give the locals warm and fuzzies that the situation is well in hand. M1114's and Mad Maxmobiles probably don't do this as well as standard HMMWV's.
We need vehicles to enter known hostile neighborhoods, let the locals know we can go where we please and challenge them to do something about it. Up Armored M113A1's can do this, but heavy infantry carriers built from modified tanks would do better.
We need vehicles to transport dismounted forces from their base to their AO. Strykers do that. Probably an armored 5-Ton could do that job, cheaper.
Bean counters and loggy toads hate diversity in vehicle fleets, but we don't have a vehicle that does it all and I doubt such a vehicle exists.