The present simple is used for a general fact which is generally, or always, true.
It is a general fact but it is one that is presently true and bears no relation to the past or futureThe fact that I might smoke cigars or pipes or even joints is not relevant, because the fact we are stating is that I never smoke
cigarettes.
Just adding some spice and possible context
This differs from the present progressive, which is used to describe things which are happening at the moment, but are most likely temporary.
We're not discussing the present progressive and I am familiar with the difference
Compare:
The earth goes around the sun. This is true now, it was also true in the distant past, and we expect it to be true into the future. It is a general fact.
Michael Schumacher is going around the track again. This is true at the moment of speaking, but the action only started recently and we expect the action to stop in the near future.
I never smoke cigarettes. This statement is one of a general fact. As a rule, I do not smoke cigarettes. And I do not intend to break this rule now or in the foreseeable future.
I disagree that this is a relevant comparison and and that there is a future aspect
I am not smoking cigarettes. This is a temporary situation. It is not normally true, but I recently lost a bet and so for the next few weeks I must refrain from smoking cigarettes.
Saying that the present simple indicates a "present habit" is just a more complicated way of saying it states a general fact.
Sure, whatever language you prefer, but it is still not a reference to the past or future.
Of course, general facts can change; but then we need extra indicators in our sentences to explain this:
I never
used to smoke, but
now I smoke regularly.
Remove these extra indicators, and the sentence is reduced to nonsense:
I never smoked, but I smoke regularly.
The sentence is nonsense because the second clause directly contradicts the first. Without the extra markers to indicate a change of circumstances, we expect the second clause to mean not only that I now smoke regularly, but that I smoked regularly in the past (at least since I was old enough to).