There's a cost to run shards - bandwidth, processing and storage. Each transaction has a 2n1 cost (2 Parties, 1 shard, 'n' shards to sync too.) Decentralizatio

There's a cost to run shards - bandwidth, processing and storage. Each transaction has a 2n1 cost (2 Parties, 1 shard, 'n' shards to sync too.) Decentralization has a high overhead to verify transactions over 'n' participants. That why centralized ledgers were created. Sharded ledgers just means that you have smaller ledgers that have to be synchronized at some point. When you have more centralization you have larger chance of fraud.