Small and medium-sized businesses should be raking in investments to accomplish a single specific and realistically obtainable goal at a time. Large businesses who haven't yet found a way to be profitable aren't going to magically find a solution to all their problems by experimenting with dozens or hundreds of new ideas at high cost, with the desperate hope that one of the ideas will randomly catch and save the business. That approach is pure gambling, and so far the gamble does not appear to be paying off.
I honestly can't imagine what people who invested in Twitter expected to see happen. I figure that with Twitter being the next most recognized name in social media after Facebook, people simply imagined that nothing could go wrong. "Everyone knows about Twitter" does not translate as "everyone uses or will want to use Twitter".