After some time like this, people must have entered Egypt who did not come with a tribe. Others may not have been of the Egyptian nation at all. At the same time, new skills were needed in Egypt as certain resources were depleted and others were discovered, and technology changed. Also, as in common, some tribes probably dwindled. All these causes led to the beginning of apprenticeship. Originally, in Egypt, this was a form of adoption. We can see why when considering the above described origin of caste in tribes becoming civilized.

Guilds probably originated in castes which had become extinct while their services were still valuable.

While economic systems have changed markedly since ancient times, aste systems have grown into class systems, but retained most of their features. While the pecking order is different from the original, the business class, military class, and intelligentsia jockey for position while exploiting the working class and oppressing outcast minorities in all Indo-european societies. Your purely economic and social status arguments fail about guilds fail to include this sort of thing, so fail to show just how fundamental guilds are to modern Western societies and how unlikely they are to be reformed.