The problem is that you generally have to compromise on decentralisation to achieve it.  The arguments in support of "stablecoins" generally hit the same wall as the arguments in support of greater throughput, except that stablecoins hit it right away.  With things like increasing blocksizes, centralisation creeps in gradually over time.  But with stablecoins, right from the offset, there's generally a central entity keeping funds in reserve to (supposedly) back the digital tokens 1:1.  While not everyone would agree, many would argue that's too high a cost to pay just to keep the price steady.