Why do brands / distributors relationships often fail?

Because they are approached like dating.

Intros are made by friends or SoMe, based on look and attitude.

What about starting from aligned objectives?

Where do you want to be with your brand in 5 years?

Do you want to be a premium brand sold just in a few top outlets or do you see yourself distributed in modern trade?

You would need totally different types of distributors.

Managing expectations are everything. I have seen great relationships starts and then fall miserably just because of misaligned objectives.

Relationship evolve during time but objectives must be kept aligned.

Pulling from two opposite ends, makes the rope break.

Brands are built bottom up, with the end in mind.