Please sell me on why I'd want to ever play a bard, when they seem so weak...

[Willie the Duck]

I’d argue that in combat the best use of Bardic Inspiration dice for a Lore Bard is Cutting Words, not granting inspiration, and that’s competes with reactions instead. Granting inspiration is still useful, but that can be done before combat begins or in non-combat settings, so again, not competing for bonus actions.

It really depends on the rest of your build. Bonus actions are that great non-constant in that they exactly as precious as you arrange them to be. If you have nothing else to spend your bonus actions on, then it is a trivial cost.