Most projects are only copying others idea and the team will stop to continue because lack of interest from investors. Another reason could be the market situation and they collected not enough for their plans.
The OP is probably talking about those projects which achieved the soft-cap level. In such cases, you can't claim that there was no interest from the investors. In most of the cases what happens is that the project team accumulates funding from the investors, and then vanish all of a sudden with these funds. In some cases, this will be done in a gradual manner. With every passing month, the development will be phased down, until they reach a point where the activity is completely stopped. In both the cases, the investors will lose their capital.