Not sure if this is true in this particular case or not but it's usually due to developer burnout. I've seen it happen over and over again.

The more exciting a new project is, the greater the risk. The initial excitement and FOMO is a double edged sword. It initially causes them to spend all their spare time on it, but this can often cause burnout and flip to an equally strong opposite emotion of disgust as their subconscious screams "all the hard work you've done on this will never pay off".