I'll preface this by saying... yes there are bike shops with very knowledgable staff.
That said, it's retail sales. I can't really even remember the last time I bought something at retail where the sales staff knew more than me. I've already researched a specific product that I'm interested in, that sales staff probably has 1000s of products to learn, well, at least hundreds. They are getting paid minimum wage and probably being asked to do the work of 2-3 people. I worked retail management for many years and watched the gradual trend of hire fewer, work them harder, and watch your turn over rate skyrocket.
The last year or so I have been unable to find anyone to answer any type of home improvement question at any of the big box places. Have you noticed an eerie lack of employees at Wal-Mart lately? Those places are are nearly devoid of staff these days. I trired to get some paint mixed at Wal-Mart a couple weeks ago. Could not find anyone to do it. Finally got a manager to attempt it, and he kept trying to call for help. He finally got someone to come and they complained the whole time that it wasn't their department (they were from automotive, which is usually well removed from the rest of Wal-Mart). The manager told them to get used to it because all employees would be covering all departments from now on. It's the way retail is going as business moves to an all online model.