I think part of Universal's strategy is to not so much to get them to spend all the time in their parks, but to get guests to see them as being the more sensible place to use as a base for an Orlando vacation.
At the moment many people stay on WDW property but travel off to Universal, Sea World, Legoland etc. as well as being locked in to Disney. Many guests, especially overseas ones, want to spend some of their vacation shopping in Millennia or Premium Outlets, or taking in the smaller attractions on I-Drive, or just would enjoy being a little nearer to the airport.
By building more themed hotels, Universal is making the case that for guests doing more than just Disney, being based in that part of town makes far more sense than trekking down to Lake Buena Vista. If those guests then spend an extra day or two than they would have in Universal's parks, then that's a bonus.