Why isn’t the pre-washing of fabrics the rule instead of the exception for manufacturers? Is it basically just a question of dollars and cents, given that it would add an operation? It would make life too easy for the consumer?
Pre-washing makes some fabrics (like denim) softer and/or helps achieve a faded, worn look. I’m not sure it would do anything for other fabrics. Besides, apparently a large enough portion of consumers prefer their jeans “new, blue, and crinkly” to make pre-washed the rule.
But it really sounds like you’re just trying to avoid washing your clothes before you wear them the first time. I don’t think I would go for that. Who knows how many underwear deprived, syphilic, toilet paper phobes have tried them on before you?
The fitting room is open.
The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik
As a home-sewist, I know exactly why they don’t. Not only would it add additional costs–lots of time pre-washing wrinkles the fabric so it cannot be laid out and cut without ironing. Then you shrink fabrics–cottons sometimes as much as 9% so they can’t cut out as many garments from a set piece of cloth.
Most fabrics shrink only lengthwise so your pants and shirts will maintain their width but will shrink in length. Some knitted fabrics do both so you get increasingly wider clothes that are too short as well. I bought a rather expensive dress made of crinkle cotton–can’t wear the darn thing as it shrunk about 2 sizes when washed as directed in cold water and line dried. If they had prewashed the material I might have gotten a dress I could have worn more than once!
I always prewash materials I use to sew with (except for dryclean only fabrics). I wish manufacturers would do the same. It’d be worth an extra dollar or two a garment for me!
Doctor: That was the gist of it, but not so much not having to wash them as the possible bleeding of the colours.
Smiling: I know very little on the subject matter. You have raised several interesting points. Glad I asked. Now, I`m a bit less dumb.
dr j… I am sorry… but I love your signature so much that I have adopted it for my own use on my email signature… anything I must pay you for use?? 
The wisest man I ever knew taught me something I never forgot. And although I never forgot it, I never quite memorized it either. So what I’m left with is the memory of having learned
something very wise that I can’t quite remember. -George Carlin
B_Line - I’d have to know much more about you to accurately answer that question, but large denomination bills are always a good starting point.
The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik