This isn't remotely true. Steel is absolutely still allowed. The steel toe is designed to collapse without crushing the toe. When that happens, the boot needs to be replaced.
There are composites which are fiber based but those aren't labelled as steel toes, they aren't designed to shatter and it's not plastic.
There are composites which are fiber based but those aren't labelled as steel toes, they aren't designed to shatter and it's not plastic.