We got them off Amazon and the fit and quality was very good. Were they custom made ? No. But they fit very well
and tight and came with styrofoam inserts that you wedge into the cushions.
Like so many other things they were made in China and the price point was very low making it impossible to compete.
We all need to remember the consumer world we are dealing with now days. While the older generation is still quality conscious
the vast majority of consumers are all about price. Never mind about quality and length of the products service life.
People are accustomed to throwing out and buying new.
Where I could see a market is maybe with the high end client who wants a perfect fit. But again this market I believe would be very small.
Check out these prices: https://www.amazon.com/s?k=slip+covers+for+furniture+sofa&crid=34Y73D3DZZ37Y&sprefix=slip+covers%2Caps%2C175&ref=nb_sb_ss_i_1_11