Your car probably has it (behind the bumper cover). Helmets have it. Your home may have it. It's light, it insulates, it absorbs the energy of impact (once at least).
I don't know if there are effective, inexpensive substitutes for those uses.
A complete idealist in me wishes that had we used appropriate material in the right places the world would have been much better place.
Using styrofoam in helmets, car bumpers and refrigerators is a completely legitimate use case as it solves more problems than it creates, but using styrofoam in cups is just such a complete waste that only gives someone a tiny bit of convenience.
For some things, it's the best material. I don't think most reasonable people would say we should ban styrofoam when it's the best material in a safety application.
For others, like food containers, it's almost purely for cost reasons when other solutions exist.
I've seen popcorn used instead of styrofoam for packing fragile thing nhsbfor ahipping. However the idea of putting a bucket of popcorn on my head to ride a bike doesn't seem that good.
That puts us one step closer to eliminating styrofoam in bicycle helmets. It may be that there are other very good or better materials that are currently too expensive, but whose prices could be brought down by widespread adoption.
I'd be surprised. It's used in motorcycle helmets as well and there's definitely a market for pretty pricey motorcycle helmets if you could claim they were better in any marginal way.
I don't know if there are effective, inexpensive substitutes for those uses.