That's a nice factoid, but if you read a little further in the logic book you would learn it's quite useful. Proving implications, such a B -> C can be an important step in themselves. It's also essential for proofs by contradiction and proofs of impossibility.

Even if you were right, that particular definition of implication is just convention. There are other logical systems and views that don't interpret it that way.

“If there was a bug in module X, we’d see this exact behaviour…”

“But there’s definitely no bug there! I wrote that code myself!”

These conversations seem pretty useful to me.