After all, how long does it take to mix a few bottles of juice?
Not very long. But they might be mixing hundreds of bottles of juice per day. Maybe something is going on with their store front (stocking inventory, a mixer quit or is out sick, their supplier was late or sent the wrong products, etc) where they've just gotten behind. Yeah, some vendors are stupidly slow and I assume these are usually one or two person operations, but they might just be bad at running a business. You never know, but they are just people too. We all demand perfect service, as we should, but it should not be seen as some major failing of vendors in general. These are almost all very small businesses. Big businesses could probably do it better and cheaper, but we don't have many or any of those right now and many members here would not prefer it anyway.
The quick reliable shippers are out there, just find them and keep a bigger stock of juice if you can afford it. Consider DIY as previously mentioned. I wish they could all be rockstars like MBV, but its just not the case.
It isn't going to be like cigarettes, where you have distributors of products produced by some of the biggest corporations in the world supplying the 24-hour convenience store down the street.