After nearly five years of development, why has "unicorn"

According to the data of the 2018 white paper on the development of Shenzhen's robot industry, the output value of the service robot industry in Shenzhen is about 34 billion yuan; the report on the development of China's robot industry (2018) further points out that the global service robots will reach 9.25 billion US dollars (about 65.1 billion yuan).
All these data point to the fact that the service robot market is expanding rapidly. This is also reflected in people's lives. Nowadays, in more and more commercial places such as restaurants, hotels and shopping malls, people can see the figure of service robots.
In fact, as early as 2015, "robot restaurants" have appeared all over China. The catering service robot has been developing for nearly five years in China, but why has no Unicorn yet emerged?
Reexamining market demand: from incomprehension, misunderstanding to understanding
For any product, the most important thing is to understand the market demand. To meet the market demand, the delivery robot needs to have three basic characteristics: efficient distribution, low cost and stable operation.
Although a large number of delivery robots have emerged in a short period of time in 2015, these products can not even meet the most basic food distribution. For example, the robot needs to lay the magnetic track on the ground, so it has low flexibility, slow delivery speed and even lower efficiency than the untrained ordinary staff. Such a robot is quite different from the "intelligent robot" imagined by customers, and even described as "artificial mental retardation" by insiders.