Various manufacturers have used plastic wash baskets over the years since at least the 80s.
When GE re-did their TL models around 1995 they had them. Frigidaire has/had them too.

I think the only reason we see some machines with porcelain or in stainless steel is to make the machine LOOK stereotypically durable.
In other words, some people think that something metal is better with no qualifiers. When the manufacturers use the metal tubs they are most likely just trying to appeal to a certain segment.

Clearly plastic wash baskets work fine.

It's just like with automobile design. In the late 80s into the early 90s manufacturers were pushing to eliminate as much metal trim, grills, bumpers ....whatever as possible.

This 1992 Taurus looks to be all fibreglass, plastic, rubber and glass with only a quick show of metal on the antennae. And it's easier to maintain, make, and it's lighter weight which is better for fuel economy.

But some buyers had these superficial ideas that metal, or at least the illusion of metal was a requirement and some how stronger, not that previous models didn't have a metal frame or parts. So a few years later CHROME Plated PLASTIC grills, hub caps, bumper strips, and a few other accents returned.

When manufacturing en masse it's all about giving the current buying public what they feel comfortable with regardless of how silly it may be in just a short matter of time passing.