There is a lot of psychology that goes into a shop layout. It's a very interesting subject. There are various reasons why shops constantly move shelves around but I'll go through a few of the main ones that have the greatest impact.
1. Promotions. The end of an aisle or some kind of 'dump bin' with goods dumped in are all about the promotion. This is actually good for the customer because they are there to save money. Yes, there is some market manipulation, and yes, its not often the best deal, but if you just looked at the aisle ends you can cherry pick your shopping and save confusion about what is or isn't included in the promotion.
2. Seasonal. Yep, Christmas is coming and its time to be hit in the face with seasonal goods. When I worked in a shop, we spent most of our time pepping and moving the store about for each seasonal event. Not even just the main events. The amount of shop space that goes over to Valentines is pretty immense. Everyone is in on it too. Your deodorants will suddenly get a new package with a heart on it, meals for two, and even heart shaped crumpets !
3. Brand awareness. One of the most restrictive things that happens in retail is how the brands control the in store space. There is a lot of money that goes into where they sit on the shelf and how much linear footage is given to a specific brand. One of the reasons why you see that bottle of Coke and Pepsi in the fridge is because they pay a metric ton of cash to be there. At one store I worked in had the fridge donated to us by Coca-Cola and every single product in that fridge had to be one of theirs, without exception. Proctor and Gamble are another dominant force, the amount of retail space they have is truly insane. They pay ludicrous amounts for the most visible spaces on the shelves. They also decide how many facings of each of their flavours they want. When they say jump, you better jump. If they put out a new flavour, it's coming with a promotional end, full range price drop and a mid shelf topper. The worst is when they change the bottle sizes. Those days made me cry.
Yep, its a huge drive to generate revenue but a lot more goes on behind the scenes than just the stores moving things about.