Understanding page-title.html.twig and/vs field--node--title.html.twig
Every page has a title, but not every page has title field (views pages, settings forms,...). Only fieldable entities (like node, user, taxonomy term,...) can use a field--ENTITYTYPE--FIELDNAME.html.twig template. 
Very often the title field of an entity is NOT the title of a page (imagine a views page showing 10 nodes), that's why the h1 is in page-title.html.twig
Modules or field formatters might use those attributes. Removing it is no showstopper, but it might have side effects depending on the modules you use. (e.g. core's QuickEdit module will not work without {{ attributes }}).