What those instruction usually leave out is the use of a hydrometer to PROVE that fermentation has indeed stopped in 7-10 days.
As most of us now realize, if fermentation can sometimes take 3 days to even begin, there is a high likely hood that it is not really done on the 7th day (come one we KNOW that the inexperience brewer will read 7-10 days and do it on the 7th, I did my first time, it's human nature.)
The kit and kilo or basic kit manufacturers are banking on the fact that they only have a limited window of sales to an individual before he/she moves on to the next step of brewing, either trying recipes in books or online, or going all grain. So the bank on 2-3 sales per new brewer before they discover how to brew beer better.
Also as you ALL know, as you became more experienced, this is a hobby about patience, but in this quick trunover society retailers know that something that takes time, would be less popular than something with a quick turn around time...So they know that even though the beer would be better if they told the n00b to wait even a week further, they want to make this hobby as "pain free" as possible....
They're not technically lying, IF the yeast takes hold within a few hours and finishes in a week, you can bottle a lower to moderate gravity beer in 10 days, as Orfy's 10 for 10 milds proves. They just leave off the fact that waiting even a week more makes for better beer.
If you've noticed, it's mostly the kit and kilo, brew in a bag or mr beer type kits that say to do it quickly. The better kit manufacturers usually tell you to wait, as well as suggest to use a hydrometer. I've noticed the the Norther Brewer Catalog gives the most accurate range of their beers based on gravity and style. They will say, for example, "primary for 14 days, secondary 3-6 months, bottle condition another 6" for a higer grav beer.
We have multiple threads about this all over the place, like this one
https://www.homebrewtalk.com/f39/ignore-instructions-do-not-bottle-after-5-10-days-78298/