Electricity is confusing to the vast majority of people which is why the average cost thing is used. I also find it annoying because I know my annual usage, I know current draw of appliances etc. Tell me unit cost and I can work it out cost of usage for myself.
But many people get confused. See the two posts above this referring to kW but meaning kWh. I’m sure both know the difference but still got confused by terminology. The average person won’t know the difference and many aren’t inclined to learn. It’s those people that the average annual cost descriptor is meant to help.
Never underestimate the capacity for people to misunderstand - plenty still think that what they are being told is that annual fuel bills for all are capped at £2.5k. It’s easy to say that it could be explained more clearly but the evidence exists for me to believe that matter how well explained this is many people all still misunderstand. I’d still like to see the proposed unit costs though.