There certainly are and have been many people who go by their middle names in the English-speaking world, but some of the examples with the first initial are rather old hand have to do with a practice common in the past among the up-and-coming sort to publicly initialize your first name but not your middle name, which was a surname that could have been an old family name (e.g. your mother’s name). For example, at the start of the comic Blondie, the name of her husband Dagwood’s filthy rich father was J. Bolling Bumstead. Do you really think his parents, his wife, etc. called him “Bolling” at home? More likely John, Jim or Jake. Similarly, the fox in Disney’s “Pinocchio”, who is portrayed as a used car or snake oil saleseman type, is called “Honest John”, but also (in some derived material) “J. Worthington Foulfellow”. Basically, it’s one monicker for one class of people, but another one for another. As a not unrelated example, US President Woodrow Wilson’s first name was Thomas and was referred to as Tommy by his parents. He apparently thought Woodrow more impressive for public life. Maybe for the same reason, an earlier president, Stephen Grover Cleveland, dropped his first name in adulthood.