Because the authors don’t get a large reward for open sourcing the work and they stand to lose future value by lowering the gate to competition. You may want th

Because the authors don’t get a large reward for open sourcing the work and they stand to lose future value by lowering the gate to competition. You may want the code, but Google will not care (or it might dislike it). Look at GPT-3+, OpenAI gets fame and fortune while people struggle to reproduce their last-gen models.