Reducing what gets into the water supply is still helpful. Rather than just letting all go into the rivers and oceans. At this point the clothing and so much material is already made/being made. Microplastics are going to be a thing for a long long time. Anything that can somewhat mitigate it is good. Reuse of a thing is pretty much always better than trashing it, at least environmentally. And never making/buying it in the first place is even better.