In 2016, I applied from Bangladesh for an Indian tourist visa; it was issued and it expired in 2017. However, I did not visit India during that time. Now I need a new visa for a 2018 visit. What do I need to do?
Plans change all the time. Not using a Visa is not at all an issue.
A personal experience. I applied for Malaysian visa, got that. But I couldn't use that visa, as my plans got changed. When I applied second time, they didn't even asked any questions. Your visa is here.
Don't give explanation on why didn't you use previous visa, unless it is asked (most probably they won't care).
There are any number of reasons does not get used. Medical problems, family matters, work issues all... these are no problem. The overall reason visas are issued are to give the receiving country a chance to research your circumstances whether you are likely to return home after your visit. Not using a visa doesn't change this at all.