Of course this raises the question, why not just develop a spell that moves your ship directly to the Astral, or open a Gate and sail through?
Simple answer - those spells require a spellcaster of sufficient level to cast them. Then your ship doesn't move without that high level spellcaster. Gate, for example, is a 9th level spell, and will only admit things at most 20' across. That's a bit of a limit if you want t move a lot of cargo...
We don't know how helms for the new Spelljammer will work yet, but broadly - By Xanathar's rules, you don't need to cast spells to make a magic item in 5e, so if you have the recipe to build the helm, you no longer need that rare high level spellcaster.