Answers to your questions, IMO are;
You cannot know if this is a common practice, as it probably depends upon company
The same goes for the reason it is done that way
It could be bad UX. Not sure how actually bad, but when user forgets password it is his "fault" and he needs to perform an action. Here user can interpret it is websites "fault" and ...
It sounds like what most likely happened is they did not want to do extra development to set up in place a different flow.
Now I consider there were two options, one to create a different flow and the second one to do some extra development.
But what would the benefits of a better flow be ?
People are familiar with the forgot password flow, it is not a ...