Is there any legitimate technical reason why rechargable batteries are 1.2 volts instead of 1.5?

Or is it just a marketing stategy so that manufacturers will continue to sell lots of non-rechargeable batteries for equipment that does not work properly on 1.2 volts. Things are even worse than they seem, as a typical non-rechargable battery is around 1.7 volts when fully charged. This means, for example, that your battery toothbrush will only spin 70% as fast with a rechargable when compared with a fully-charged non-rechargable.
I’m extending this, because I’m not convinced that patagonia’s answer is entirely satisfactory. Why did they choose a compound that can only be charged at 1.2 volts? They used to make rechargeable 1.5 volt alkaline batteries, they just weren’t much good. If we can send a man to the moon, surely we can make a decent 1.5 volt rechargable battery???