Why is it so abstract? Please forgive me for asking an open ended question.  

Are there various resources that explain WHY different changes were made? I'm getting used to the idea of YAML and TWIG files. I'm just struggling to understand WHY they moved. I'm supportive of learning a new way.  

To me, it seems like they took the old TPL files which were decently easy to understand and replaced them with the alternate syntax from TWIG. 

What is the functional/practical benefit? is there something I can read or watch to get it?
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.