Why are some first names always abbreviated and some not?

Is there any consistent rule or at least an explanation why in some names the first name(s) are traditionally nearly always abbreviated and in some are not?

Why, for example, T.S. Eliot but Thomas Wiseman,

or H.G. Wells and not Herbert Wells;

Charles Dickens and not C.G. Dickens or something?

Obviously, both forms must be correct, but in practice only one or another appears for a particular name in writing. And it mustn't be the first name that affects it, as the first example demonstrates... (And let's stick to real names, as opposed to pen names, which can be anything).