Probably a risk worth taking; defending a pipeline is much easier than escorting huge, slow-moving ships through a 24km-wide Strait laced with mines and peppered by artillery and missiles.

As opposed to a single continuous structure in a well known location, full of flammable liquids?

Pipelines can be protected. Just putting it in the ground for example. Or you build a "bomb" proof shelter over it - Iran's missiles are not bunker busters, we know how powerful they are and can design for that. Air defense systems are getting better too.