Because MM will go last in order, it will cauise:
1) In case of tie-breaks, losing "tech" wonder
2) Allows leaders having their turn before MM to make certain actions slowing in some way MM's research, fe:
a) war declaration on MM, so MM will change his civics to less scientific;
b) pillaging, taking his city decreasing in this way his research power
c) most important: trade techs with other leaders instead of Mansa knocking to ones door. Also make demands (especially gold, so Mansa will not run his turn on 100% research)
3) As stated 2 post before - gives an opportunity to trade his new techs as a first leader
etc. etc.
It would not make him backward, but can have a slight impact