Why is ammonia in cigarettes?

Allowing for the very likely case of a mis-spelling in your question, I will assume you mean "menthol", which is in the cigarette paper in menthol cigarettes. Some smokers prefer the menthol sensation - simple as that. The Word "methanol" in your question is methyl (wood) alcohol, and is not in cigarettes in any more than minute trace amount, if that. There are supposedly 4,000 different compounds in cigarette smoke in "minute, trace amounts".