1. Mars is the ultimate tax haven - Think about it, there are no taxes on Mars meaning people could go and live on Mars or have their companies on Mars meaning that they pay no tax which is very bad for the economy. Having an Emperor on Mars would make it very hard for someone to us it as a tax haven.

2. Anyone can build anything they want on Mars - There is no local council on Mars meaning no one needs any planning permission so Mars could become a hotspot of conservatories (Which everyone knows are the worst invention in all of history)

3. There is no official representation of Mars - The people of Mars have no voice in the wider politics of the Solar System which could cause a lot of unrest which could lead to rebellion, and nobody wants that.