How are ionic formulas written?
There is no other Ba(OH)x so there is no need to note a difference between several forms.

This happens with any metal ion that only attains precisely one positive charge, whether it is +1 or +10.

Lithium ions have +1 charge. Carbonate ions have -2 charge. Therefore to balance the charge in the formula we need 2 lithium to 1 carbonate.

This happens with all formulae, and it is a simple mathematical check to decide what the correct ratios should be.