Because that is the paging that Phorge performs by default in this case.
Several users in our installation were surprised that they got 100 results and "some tasks were missing" though they did not set any value in the Page Size field in the /maniphest/query/advanced/ search form.
Upstreaming from https://phabricator.wikimedia.org/T288915
If this is the only place where we have a "limit"/"page size" field, maybe just remove it?
I'd really prefer not to do that. I pretty often need to work with complete search results (e.g. batch-editing), not with only the first 100 and then repeat all steps for the next 100.
What kind of operation are you doing that involves loading all tasks in a browser?
batch-editing still requires you to manually shift-click on each item in the list - is that what you're doing?
Housekeeping: Mass-removing or -replacing project tags when code projects moved to a different team (and thus team project tag), mass-resetting assignees (when someone left the organization), etc.
Note that I do not load "all tasks" (if you really literally meant that) in a browser but my search criteria often lead to more than 100 task results. Thus I'd like to keep the "Page Size" field to be able to manually set a number higher than 100, and I only want the "Page Size" field initially to reflect the fact that Maniphest Advanced Search has a default pagination of 100 which has not been obvious to some of our users.
batch-editing still requires you to manually shift-click on each item in the list - is that what you're doing?
Under "Batch Task Editor" at the bottom, you can click "Select All" and then "Bulk Edit Selected >>". There is no need to manually select any tasks except when you want to manually exclude some tasks from your search results before performing a batch edit.