Your question seems to be based on the assumption that each verb construction (present simple, present continuous, past perfect, etc.) has a single usage (or definition). This is certainly not the case.
It is true that "we use the present continuous to talk about actions which are happening at the present moment, but will soon finish". But the present continuous is also used for present happenings that will continue long into the future.
It is also used to talk about the future in the context of some arranged action:
- I'm playing tennis with Jane after work tomorrow.
In the cigarettes example the present continuous is used to express irritation:
- You're always cadging cigarettes from me.
Collins Cobuild English Grammar (p249) states:
5.24 The present continuous is also used with adjuncts of frequency when you want to emphasise how often the action takes place. This is
often done to express disapproval or annoyance. The adjunct of
frequency is placed after the auxiliary verb.
- You're always looking for faults.
- It's always raining.
- And she's always talking to him on the telephone.
- They are forever being knocked down by cars.