Because it's awesome.
1. You can clean them any which way you like: warm water and soap, toy cleaning spray, disinfecting wipes, 10% bleach solution, dishwasher, etc.
2. Because of reason number 1 (and it's material safety rating) you can share this toy between partners and orifices safely with no transfer of bacteria, after cleaning.
3. You can use absolutely any lubricant you like with it.
4. You can warm it up with warm water or cool it down with ice water for temperature play.
5. It's downright sexy and makes a gorgeous glass piece of art on your desk (if you're brave enough or it's discreet enough).
6. It's hardness makes it very satisfying for anyone wanting to feel "filled up".
7. They can be used for body massage, depending on the size, shape, and texture.
8. They can be used in the water, won't set off metal detectors when travelling, and are hard to break.
9. They last forever!