GardenWalk was a bad investment in 2001, in 2009, and would be still so today. Those outdoor malls are a dime a dozen now in southern california and there are plans to build even more (OC Vibe) right down the street. Had Disney bought it before, they would have been saddled with running a failing mall, negotiating the hotel development agreements, and paying off debt before doing what... spending more money to flatten the whole thing for some other use? I don't think it was every going to work out financially to buy that land.
It's not as valuable to them. Not now at least, I don't think.
They're not going to build a third park in Anaheim. With DisneylandForward they have already made their intentions clear: they want something new. A Downtown Disney with rides and entertainment. Something that can be a mixed-use development that they can grow into gradually, rather than committing billions of dollars for a theme park that will just need to be fixed as soon as it is built.
I highly suspect that their first play here will be slowing adding attractions attached to the current Downtown Disney area that are pay-per-ride fee based to test the waters. If it goes well, they will expand into the Downtown Disney East (Toy Story Lot) with more shops/dining/hotel/rides all mixed on one property. That plan doesn't require huge chunks of land be available at the onset, so they can acquire expansion space if and when they need it.