It happened to me several times that collaborators let me work extensively but then stopped responding. This seems to be also the experience of others.

The first step is to not blame yourself. None of us knows what another person is going through — perhaps the ghoster is dealing with a truckload of stress. Maybe they thought they would respond later to your messages, but then the right moment never came, or your e-mail got buried in their inbox under an avalanche of other messages. Or perhaps they no longer wish to work with you and are trying to spare your feelings by not saying no directly. It’s impossible to know, so there is no point in blaming yourself. They made the decision to ghost you — but your reaction is entirely up to you.