Seems to me, everybody (especially LauraFrog, as always) commenting is right - but I suspect the main points are the fact that they are businesses which do exist to sell things - and that even informed employees haven't got time to subject each customer to what's likely to be perceived as an insulting quiz.
Imagine the line-ups of people waiting hours while each of them were put through the mill - then try to imagine them coming back to do it again, every time...
The LFS I most often go to has people so busy caring for the fish and other animals that it's often very difficult getting any assistance for humans, which is how it should be - but can be tricky when people driving are nice enough to stop by after shopping or whatever are waiting for you to be done, and complaining about the length of time spent doing so.
Add in several hours for the rotational quiz show,,,
These owners/employees don't have enough time in their work-day to do whatever they already do, never mind extra.
Specific people would have to be hired especially for the purpose of delivering lectures and qualifying/disqualifying people wishing to make purchases, something no individually-run store could afford to do or any big chain spend money on.
Considering the vast number of animals passing through their hands, pet store people can't, obviously, be expected to all know all details relevant to each particular fish carried - that's up to the purchaser, although not all fish-keepers have access to the internet - or have time to sort through often differing advice on multiple sites, or have the awareness that much misinformation is circulated and often generally accepted.
And considering the amount of misinformation common among pet store employees, I, personally, would be unlikely to take the advice of any, unless it chimed with what makes sense to me.
Once somebody, in nightmare example, has recommended Melafix as an ich treatment, or states that bettas don't need heaters or swim-room, or states that a betta with blackened blobs on the stumps of ruined crowntail extensions doesn't have fin-rot but 'is just like that', and endless cetera, I've rather lost interest in seeking advice.
I really think sites like this, although only available to those with internet access - and threads like this, drawing attention to such problems - are about the only feasable answer to the problem.
Edit - part of sentence fired as redundant, sign of the times, lol, that and I evidently can't spell.