One business element is simply competition. 5e has to compete with PF, OSRIC, along with a host of other RPGs out there. The OGL has established a market environment where there is plenty of free rules. Stepping into that market with a one-to-one correspondence between purchased product and consumer it's a bit of an uphill battle.
Not only are they competing with currently produced material, but they are also competing with older material that is also free, and a culture that has developed with an expectation where some of the material is for free. If they show up with 5e and say, "we made some new stuff, but you need to pay for all of it if you want to play it" then plenty of gamers will just shrug their shoulders, say "whatevs" and go about using existing material, or gravitate to something that will give them plenty of free stuff to entice them into a product range.
If they want to win back people that left D&D behind in some fashion then they have to create an "accretion zone" which will draw gamers in. A big part of that is through peer connections. If you have one person who's intrigued by 5e then the best way to draw six other people along is for them to be able to just send a hyperlink to an online SRD to get the other players interested. Otherwise it's a lot of negotiating, people hemming and hawing over cost, etc.
I've seen this at work with Pathfinder. I've roped a lot of people into Pathfinder through the Pathfinder SRD website. Some of my friends complained about "I don't want to have to buy another million books!" and I'd say, "you don't have to, Paizo makes all of their rules material OGL and free" at which point they started to consider it and eventually got hooked and started buying stuff.
It can't be stressed enough that a 20 year old business model where people have to buy every product produced by an RPG publisher just doesn't work anymore. The market has changed and there is so much competition for dollars, not simply within the tabletop market, but from every other media format also.
There is also the broader tabletop market. If they want to hit their big revenue targets then the RPG market as a whole needs to grow. That means they need to make playing the game as accessible as possible. People can play RPGs, which requires a lot of time, energy and scheduling with others to make it work, or they could just get Skyrim, or Battlefield 3 or whatever new MMO is out and have hundreds of hours of play. Sure there are trade offs, it isn't tabletop, but there is plenty of media out there now that is compelling and doesn't require the kinds of hurdles that tabletop play has.
So you need to strip away barriers for people to enter the tabletop market or keep them there, or draw a D&D player back who has a zillion other RPG options to choose from.
In terms of profit they have to draw them in with free stuff and then hook them into a DI experience that can't be found anywhere else. They roll out a strong virtual tabletop, they produce apps for iOS and android that lets people use tablets and phones at the table in robust ways, they give people access to a wealth of art, sound files, map making programs, etc. Make a really strong and integrated digital package and that accretion effect will start to kick in and people will begin to glom onto the game. WotC has the deep pockets to do this stuff which other people in the tabletop industry can't pull off.
For me I find it harder to imagine how they could possibly hope to surpass 4e's revenue if they took a dinosaur approach to the market, expecting everyone to pay for all of their products. It doesn't instill enthusiasm or loyalty, just consumption, and eventually people will have full tummys and wander off.