Obviously to avoid losses, that is the most logical reason why would they do that, if for example an ICO seems to have a good idea a good project and a good team behind, but it does not seem to be so popular the first thing people would is sell their tokens as soon as it goes on exchanges, in order to cut their losses, and i see how this can be a real concern since it can actually kill a lot of good projects, so holding would actual help it and make their investments worthwhile.