The puzzling aspect is that, contrary to what most people would assume, the B, I, EM and STRONG elements all came out under the same version (2.0) of HTML: https://meiert.com/en/indices/html-elements/
No, there is a clear distinction between typographic and idiomatic markup. The i and b elements are considered typographic elements, not idiomatic ones (as em). So newer standards actually made them idiomatic.