For the same reason they use "tokens" instead of kilobytes: so that you don't do the conversion yourself and realise that for example spending a million "tokens" on claude-opus-4.6 costs you anywhere from $10 (input tokens) to $37.5 (output tokens). Now, 1 million tokens sounds pretty big and "unreachable" until you realise that's about 4 megabytes of text. It's less than three floppy disks of data going back and forth.

Now let's assume you want to send a CD worth of data to Opus 4.6. 700 megabytes * $10 (price per million input tokens) / 4 (rounding down one megabyte to roughly 250k "tokens") = $1750. For Opus 4.6 to return a CD amount of data back to you: $37.50 * 700 / 4 = ~$6.5k.

A terabyte worth of data with a 50:50 input/output ratio would cost you $5.7 million. A terabyte worth of data with a 50:50 input/output ratio on gpt-5.2-pro would cost you $25.2 million. (Note: OpenAI's API pricing still hasn't been updated to reflect 5.3 prices.)

So we get layers upon layers upon layers upon layers upon layers of obfuscation to hide those numbers from you when you simply subscribe for a fixed monthly fee!