First, shards are used for network scalability, the network is using one shard at the moment.
Furthermore, there is about 2 tx per second in TON currently. (In mid 2022)
One shard is able to process around 100 tps and start to split to subshards around this value. So there is not enough load for many shards. There were actually 16 shards prior 9m blocks (due to global split params) and also some spam events as well.
More detail about Share Chain can take a reference in this reply: