Bike porn

I understood! (I think)
The tube is the same thickness throughout with no butting even in areas that aren't put under enough stress to warrant it that wall thickness?

The main point, I think, is the ease of production.

Some dont even have the fatter tube top. Just a tube with a mitered end, and a hole, cradle, clamps an bolts. All the components fit any diameter tube. So you can run off a load of diffrent lengths and sizes, without the need to diversify your hardware.