It is the logical place for adding it.
Based on experience elsewhere, I have long suspected that thinking up a Title after the body of a Q has been written is likely to lead to better quality Titles. I have been known to scroll down to add a Title first (which I have not found bothersome, though that could be because I write few Qs) but even so I may well change it after I have written the body.
OP wrote "I assume that most folks' thought processes starts with an idea, a vague question and then it develops into something more, a body that includes a context." With the sequence "vague question" > "Title" > "a body that includes a context" it does not surprise me that Titles can leave a lot to be desired.
Springer has advice about Titles (though the context is scientific publications rather than Q&A):
The title of your manuscript is usually the first introduction readers have to your published work. Therefore, you must select a title that grabs attention, accurately describes the contents of your manuscript, and makes people want to read further.
It does seem likely to me to be easier to describe content accurately after such content has been written, not before. A scaled up analogy might help: "What describes a ship better, the plans sent to the yard by the naval architect, or the 'as built' drawings?".
Advice here includes:
the more you repeat the title, the more boring it gets and the more space it wastes
It did not work in this case, but hopefully adding the Title after the body will also sometimes help reduce clutter. I this case the 'thought process' seems to have been write most of the body, then ask the Q, and finally copy the Q into the Title box (and add tags). The unnecessary repetition is unfortunate, but the actual order of events in this case seems to have been exactly the sequence the current layout seeks to encourage.
Placing the Title box after the body puts it adjacent to tags. This may help improve Titles by reducing tags in Titles and hence make Titles more meaningful without adding to their length.
Originally "Why does the title comes after the body?" (in the body) does not evidence a great deal of care. The incorrect grammar is perhaps something than can't be helped but clearly that this was only intended to refer to Qs does not come across in that version of the Title. OP seems to have found it worthwhile to edit the Title to include when writing / editing a question, but that is now incorrect.
Here is an example from yesterday from a site where the box for the Title comes first:
Google Sheets: filtering and matching a list treating NON-unique values
It is from a site where [google-sheets] is a tag and a site that actively discourages tags in Titles. Hopefully, if only now and again, some users will realise when going straight from something like the above to choosing a [google-sheets] tag for it (i.e. Title below body) that the Google Sheets: is just a waste of space. The saving might only be a few characters but even these could be useful. That no A has yet been offered there may already indicate the Q is not clear. filtering and matching a list in the Title may make sense when the Title is prepared before writing the body (where FILTER and MATCH functions are shown in a formula). However much less so when the Title is prepared after writing the body, and the body finishes with "I'm starting to think filter and match are the wrong functions to use for this."