1) I'm not surprised that Disney hasn't marketed the Magic Band system. it's still in test phase, and the program is still in flux. The changes announced today are a good example of that - with no warning, they changed which rides you're allowed to book and when. If they had announced MBs to everybody and hyped it, lots more people would have been upset. I'm sure they'll hype it more when it's good and ready.
2) If attendance is already high and at or near capacity, there's no point in building MORE rides. The parks are already FULL of rides. The only reason to build new ones is to replace old rides that are no longer attracting people. In Disney's ideal world, there would be no Universal or Harry Potter to draw off guests, and they could just keep maintaining the same rides forever. Besides, many of the oldest rides are the best. I'm middle aged, and the best rides in WDW are all older than I am (BTW, the 4 best rides in WDW are BTMRR, SM, HM, and POTC. If you have a different opinion, you are wrong, and I will brook no argument!) So, at this point, if Disney can do something to change or improve the experience for guests and makes them more money than a new ride would, more power to them.
3) The parks are NOT getting more crowded. After a slight decrease during the recession, attendance at most WDW has been up about 2% per year over the last few years. You're simply not going to notice 2% per year. Any perceived difference in crowd levels (especially over the past few years, as some are claiming) is due to something OTHER than overall attendance - such as changes to the yearly schedule, major events, psychological factors, etc.
4) Disney is doing this so you'll spend more time in the restaurants and gift shops. That's the REAL reason for doing this. It's not about "marketing" to you. If it was about marketing, it would be a two-way system, where Disney would be able to communicate its marketing message to you. Magic Bands can't do that. Yes, Disney is tracking you. But it's not tracking you, personally, it's tracking your data. Who cares?
5) If you're in line, you're not spending money. Most people would be happier doing something other than standing in line. So, Disney kills two birds with one stone - they make money, and guests are happy with shorter lines.
However, as a previous poster pointed out, the lines are a form of crowd control. I seriously wonder how much Disney thought about that. It's beginning to be my #1 concern about the FP+ system.