If the main reason of using Story Points is to get team's velocity and plan future sprints correctly and resourcefully... why is it considered that only Stories should have Story Points?
Our sprints consists of Stories, Tasks, Bugs. How can we get team's velocity if only Stories will have Story Points
In continuation to your previous question, you have the option to add the Story Points field to other issue types like Tasks or Bugs. You can do that by modifying the screens used for those issue types and also looking at the context defined for the field story point. You can ask your Jira Administrator to do all that.
Jira won't stop you from using Story Point field in other issue types. You just need to spend some time working with your board to see how this field affects your way of planning.
I hope it helps.