This is just business, and is not unique to photography. I'm a electrical engineer and have a consulting company that also sells small gizmos on the side that I designed. I won't sell you certain things directly either. The broad reasons are the same regarless of industry.
For example, we just got another lot of 1000 made of one particular gizmo. After adding up all the costs, these cost us $3.95 each to have fully built, tested, delivered to our office, and includes the cost of managing the build process. We sell them to one reseller for about $10.50 in lots of 10s to 100 or so and they resell individual units for $14.95. That's actually a very small reseller markup, which is because they take them on consignment. In other words, they don't pay for stock, but pay me once a quarter for units sold, usually with a order for what they think they need to replenish stock for the next quarter.
There is no way I'd sell you one, even for the $14.95 full street price. The $11 profit just isn't worth the hassle of putting it into a box, shipping it, accounting for and charging you the postage, etc. If we sold 1000s a quarter we could probably afford a lacky to pack and ship boxes, but the volumes don't justify that. However, the real reason is you'll expect my attention and support that will greatly outweigh the $11 profit.
In another case, we sell units that cost us $17 to produce to resellers for $36, which they sell for around $48 while we publish a list price of $59. Even if you wanted to pay me $50 for one I'd refuse for two reasons. First, you're going to suck up my time. Just one phone call and whatever profit I made is blown on lost consulting time. Second, I don't want to undercut the resellers. I need to let them make a profit selling my stuff, else they won't be selling it. If I regularly take business away from them, then they aren't going to make money and will stop selling my product. The $12/unit they cost me is well worth the publicity, front line support, and fulfillment they provide.
I expect the business logic behind the photo albums to be basically the same. They are not set up to deal with and support the end customer, and need to let their resellers (the professional photographers) make a buck on their stuff, else those resellers will go resell something else. It's just basic business.