Two people are walking towards each other along a crowded pavement. Each is carrying a precarious pile of boxes in front of them. They see each other coming, and as they approach engage in a careful dance to get past each other without dropping anything. They succeed and carry on about their days. No one else notices or cares.
Another two people approach each other on the same street in the same circumstances. They look at each other's boxes and are a little intrigued. There is a relationship between them. It slightly distracts them. They collide and their boxes fall to the ground. Now they have conflict and opportunity. Sparks might fly. Confusion might grow. People will watch and make judgements, some of them harsh. Things aren't under control.
Too many "collaborations" are like like the first, and get judged a success. Two many of the second kind get dismissed as pointless.