Adding silk touch would make a way for player to mine or blocks in the open seas and then taking it back to there island to use vein on the ore block, also it would be nice to be able to mine ice, grass, mycileum, etc.
There is a silk touch enchant for spawners called Spawner Touch, but other than that we do not have much of a need for silk touch. There isn’t enough naturally spawning stone or blocks that when broken are something that requires silk touch.
Considering those aren’t naturally spawning blocks on our islands, I still don’t see a purpose. The ice I assume was put there by a Special Snowflake which means there are intentionally placed blocks.
Ice is not that expensive, just buy more.