Why do some reviewers mention their decision explicitly? Recently, some of the reviews I received mentioned their decision at the end of the review (i.e. 'I recommend acceptance of the paper'), while others do not have such statements.  

What is the point of adding the decision statement while the overall evaluation (i.e. on EasyChair system) explicitly says it? Is it just the reviewer's habit?
Typically I include an explicit recommendation in the report to be shared with the authors when I have a strong opinion, but not necessarily otherwise.  In the former case, the editor can still decide either way (referees make recommendations, not decisions), but if they disagree with me at least the authors will know for sure what the referee thought.


  what is the point of adding the decision statement while the overall evaluation (i.e. on EasyChair system) explicitly says it? is it just the reviewer habit?


It may be habit, and it may reflect uncertainty about what information from the web form will be available to the authors.