But would manufacturers want to market such a product, given the attractiveness (to them) of their gels and shampoos that so quickly end up down the shower drain?

They often infest shower drain holes, where proteinrich residues from shampoo create a slimy habitat.

The leeches end up washed down a shower drain, where they grow to enormous size and return for more feedings.

Many guests have long hair and the shower drains quickly become clogged.