Do Isotopes occur in all elements?

As far as "why carbon has isotopes", who knows. But C-14 is the most common type of carbon isotope. 14= Atomic m. 6 Protons, 8 Neutrons. Since C-14 is slightly radioactive, its the key factor in carbon dating. BTW, Carbon dating can only be accurate for up to 50,000 years. Radiometric dating, which uses elements such as Urianium and Radon, can be accurate for billions of years