Why didn't Lego sue so many manufacturers for copying Lego?

Yes, but I lost several times. Lego applied for a patent for building blocks a long time ago (I forget the specific time, at least 198 years ago), and then the patent expired, because the design of Lego building blocks was too normal and the patent was not extended. Personally, I am Lego powder, which means nothing about black Lego. Personally, I think there are few kinds of building blocks except Lego, and plug-in building blocks can only be made like Lego. After that, several American companies began to imitate Lego. The cheap building block is Lego, which has lost a large market. Lego is expensive because it uses ABS plastic, and its processing technology is also expensive (copyright is later, later). The director of Lego insisted on ABS from the beginning, because he wanted to make safe, non-toxic and non-fading building blocks, and Lego parts would be washed with water as new decades later. But after all, Lego has no patent, but the manufacturers who copied Lego are also formal. Later, Lego ventured to regain the market by buying various copyrights of movie animation. After all, Lego is mainly aimed at children, and children certainly know the difference between Lego's building block movies and other building blocks. As Lego retakes the market, its high quality and excellent design are also reflected.