What being a vegan is about is up to each individual themselves. There is no kind of contract which allows you to call yourself or see yourself as a vegan, and its furthermore very tiring when someone's trying to preach to you what veganism is about <fill in strict ruleset here>.

There are different sorts of vegans with different reasons for their dietary choices.

And regardless, for some, after avoiding animal products for a long time the thought of eating them can come to be unappealing.

There are three global reasons one can decide to be vegan, vegetarian, and reducetarian.

1) Animal well-being.

2) Environmental well-being.

3) Personal health well-being.

You may substitute well-being with suffering, and there's also a nuance between death and staying alive but using (e.g. milking).

[EDIT: I suppose there's a fourth, a psychological reason how some people find certain products 'impure' to eat. But I'm not sure how I'd define that group.]