This stuff was stored before the reset, when after March 31st, beacons were 200$. He stored it by spawn because spawn wasn't being reset. And @Domino13 has probably more than 2 stacks at warp impoor.
In lost islands, bedrock was actually allowed. It was known as a money maker but you could also just make shops like usual. Each bedrock was about 15$ each back then but I was only a non-donor. Then slimeballs then nothing. thats the story of currency with bedrock and slimeballs.
Emeralds are made rare on purpose, to prevent people from ruining the economy of yet another item. Besides, the block would have to be worth at least $200.
The only blocks that would be added into the shop at spawn would be items that are not legitimately obtainable from kits or other resources.