Wouldn't that be totally 100% up to the preferences of the reader to decide?

Why would the site support multiple view options, unless the forum owner thought both alternatives would make sense for different readers?

If a thread have 100 posts - why would I like to visit a thread and look at one comment 10% down the tree, another new post 55% down the tree and a third new post 80% down the three? With chronological order, the last page of the thread will contain these three posts directly above each other. Quick and easy to find.

Besides - quite a lot of people who do make a response to another response quite high up in the tree does it based on information he has from having read the full tree. So that post high up at start of tree do cover subjects at way different parts of the tree. Corresponding to the chronological view that tells exactly how many posts that did exist when that post was added.

In my view (I'm allowed to have a view, don't I?), it's better to read threads in chronological order for at least 90% of all threads. Then now and then, someone manages to create an old "back-burner" sub-thread somewhere high-up in which case a tree view could be better. But obviously, I do set my preferences for the reading style I feel is better for 90% of the cases instead of setting a preference for something I feel is better only for 10% of the cases...