If you had more throughout, more bit depth, etc you would have enough colors to not see banding. But the bitrates required (if you insist on 4k) are tough on SSD/HDD IO to say nothing about your network connection. And even if you have the best connection ever, most people don't and streaming services will want the bitrate to be as low as possible as long as the average viewer is not too upset, because delivering higher bitrate costs service real money and most customers don't have the connection for it and don't care about banding