A habit is not necessarily bad to have and it does not have to turn into an addiction. A habit that is based on an interest that is productive or a passion that leads one into a life work is a positive activity that is habitual but that is for the good.
It can be difficult to get started on something new. For example, a new diet, or a new hobby. However, if you continue to do something regularly, such as every day, and perhaps even at the same time every day (such as, maybe knitting every evening), then it will eventually become a habit and something you do almost without thinking. So pursuing interests regularly can lead to them becoming habitual.
It is normal and very habitual to pursue your interest on a regular basis. It is human nature to not only pursue interests but to make a life our of what your interests are. It would be very, very weird to consistently pursue things that you were not interested in.
I believe it is natural for people to habitually pursue their interests. Humans tend to create goals in all facets of life, regardless if it be something simple or something very complex. I may have a goal to complete college while at the same time hold a goal to drop a piece of mail off at the post office. I believe people will always follow their interests, because life becomes more troubling when you don't. Generally it takes some sort of goal to pursue interests, so I think they are very common ideas.
No, it is not habitual to continue to pursue and interest, because it is simply a matter of instinct to do what a person thinks will make them happy. That does not mean they are doing it out of habit. That means that they are just making choices that they think will make them happy. They obviously think their matter of habit will make them happy.