Why is there not pre-thinned paints ready for spraying?

Do you want to pay paint prices for more thinner? Most thinners are considerably cheaper then finishes so if you sell a 'thinned' finish you probably be paying paint prices for the volume of thinners that are in the thinned finish. Plus there is probably no universal amount of thinning that would work for all applications so you'd probably have to thin out anyway depending on your application.

Why would they?

there are different thinners. Some for humid conditions with retarders to prevent blushing, some for dry that prevent orange peel.
Also by providing you with the choice of thinners you get more solids and a much larger supply.

Is it that hard to thin your paint?

Is your name INSTANTsiv indicative that everything must be done in an instant.

Also by controlling the amount, and thinner type you can do different things.. But I won't get into that, its complicated.

And in answer to your question, no it doesn't shorten shelf life.. I add thinner to some paints when storing my paint to prevent it from hardening.

That makes sense… Too much variation to have a product or range of products to work broadly across different materials and equipment.

@woodchucker, I don't thin paints so I wouldn't know if it's hard or not. I asked because I see the question a lot. Also don't read too much into my name, it was a captcha that I got once and I liked it.

While it may not be cost effective, it would be convenient and there would be people to buy it. One problem would be though that certain sprayers need different viscosity.

I use createx wicked colors as my paints. No thinning required, though I do sometimes for different effects (color fades).
They're waterborne airbrush/automotive paints, but they work great on wood as well.
They do require a clear coat, but I'd be doing that regardless of paint used.

It's even more basic than that. The additional cost of shipping. The extra weight cost's money. Plus diff sprayers can spray diff viscosity's. I know my 4 stage turbine handles things diff from my old hvlp. There is no one size fits all.

I can spray right out of the can using an airless air-assisted pump. No thinning needed.

Sometimes I'll thin 100% for use inside an airbrush. HVLP applications get perhaps 10-20% thinner at most. Pre-thinned finish would be hard to use considering the thousands of spray equipment combinations in use.