HEIC is this plus a kitchen sink of features for digital camera rolls, which aren't useful on the web, all wrapped in a ton of legacy ISO BMFF complexity reaching as far as Classic Mac Quicktime. BPG structure is much more minimal and pragmatic.

However, BPG is unnecessary nowadays. Modern browsers support AVIF, which is HEIF+AV1, so basically HEIC with the painfully patented bit swapped for a freely licensed one.