Thinner glass is actually less subject to the effects of thermal stress, as low thickness minimises temp differences between different parts of the glass (this is why people can make vapes out of soda-glass light bulbs). It's differential thermal expansion that causes heat stresses, and if the material isn't as thick, it's harder for one side to be much hotter than the other.
The heater has to work through the glass, so, since glass is actually a pretty good thermal insulator, it can't be too thick, or the device would be really sluggish to react to changes in draw speed. That said, I'm surprised the parts of the tube where it's clamped into the unit at either end, and especially the bit supporting the ground joint aren't much thicker than they are. Only the section around the heater needs to be thin. If each end of the tube were reinforced and well-anchored there'd be a lot less bamboo breakage.
