What Makes an Rv Fridge 12V

My previous rvs all had three-way refrigerators. My latest one is only LP/110. What makes or what made the rv fridge 12V and why are they not common anymore?

Can an rv fridge be wired for 12V or is it not that simple? Yes, I know I could run mine off of an inverter using my solar while traveling.

I miss the option of 12v.

Thanks in advance.