1, Youku has been infringing, but he used the principle of safe haven to say that he needs netizens to report him before deleting infringing videos. Perhaps it was because someone later reported or related video websites sued Youku for infringement, so you used to watch it, but now you can't watch it.
2. At present, Youku seems to have changed the leadership team to correct the previous infringement, so now you can't see many videos and movies in Youku.
As for what you said, "different companies have different copyrights", every video company, such as Youku, such as Tudou, can buy the copyright of the video from the original author. In addition to the different buyers, there is also a question of whether to buy permanently or only during the hot broadcast period. Maybe the video you watched on Youku will be deleted at the time of purchase, so you won't be able to watch it.
4. Can you see these videos on other websites? Have you found that these websites are generally small and don't look as formal as Youku or Tudou? The reason is that their share in this industry is too small, and the traffic is too small, which harms the interests of the infringed, so the infringed has no time to sue them or the infringed has not found them yet, so that you can see videos that Youku can't see on other websites.
Finally, I want to say that the Internet in China is developing in a healthy and legal direction. I hope you can watch as many legal videos, movies or TV dramas as possible. I hope what I said is helpful to you.