It's the law.

When one bubble meets another, the resulting union is always one of total sharing and compromise.

Bubbles always have the minimal surface area, and so share common walls where they meet, kind of like attached housing. 120 degrees is a magic number, the meaning of which is known only to mathematicians, bubbles, and bees. But bubbles always meet at intersections of 120 degrees. So do the cells of honey combs, but that's not relevant here.

These bubbles are blissfully ignorant of the 120 degree law, and so cascade out at whatever angle they please. It's contrary to the laws of physics, but it makes for a great intricate design by artist Eldar Gousseinov.