Ok, I’ll bite. I will say up front that I’ve never felt that I needed a Scrubba on a cruise ship. If there’s a laundry service, sign me up. I do, however, travel to moderately remote places - moderately meaning running water but no laundromats or fluff and folds. So how to get dirt out of our clothes when when we’ve been getting filthy on a geology field trip or archaeological dig? Scrubba.
Pre-Scrubba, I used pretty much the same technique described. I think the Scrubba’s useful, not everyone would find it worth the space. Oh, and It is first rate for getting chlorine out of swimsuits.