More expensive and not worthwhile are two different things. Also when certain implementations become popular it's much more likely someone will write a very efficient kernel for decoding said text making it much less expensive than generic OCR.

Also more expensive doesn't mean that something won't happen, only the dynamics of how it happens. For example if you put all your documents in images then some service might just sell the AI providers the text. That service may do underhanded things like bundle OCR in an app that does something else and use your phone to get the text out of these images all day.

It's slightly more expensive, but the cost would be worth it if this became common. It's not designed to be hard to OCR, it's designed to be hard to copy out of the source code, so it doesn't require a very advanced OCR system (and all the regions that would need OCR-ing are clearly marked).