Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Smoking is forbidden for many reasons which we discussed thoroughly in our Fatwa: 81589.
As for soft drinks, basically they are lawful unless there is a reason that makes them unlawful like causing drunkenness or considerable harm, etc.
Know that, when we cite harm as a reason for being unlawful we realize nothing is free from a bit harm, but we mean a prevailing harm or a harm which is more than the benefit; otherwise, a little bit of harm is not taken into consideration.
Thus, there is no way of comparing between smoking and soft drinks. When it is proved that the harm in soft drinks is greater than that of smoking then they become forbidden.
As for why smoking is spread in a Muslim country, this question should be addressed to the authorities there.
Allah knows best.