Why is it so abstract?
From what I understand there are two primary reasons this was done. The first was because people were using templates incorrectly - they are supposed to be templates, not logic files. People were putting lots of logic into the tpl.php files, when any logic should be in a preprocess function. The other reason is that TWIG escapes data, preventing people from putting bad code into a template, making Drupal sites more secure overall.