Obviously, in China, fish sauce is generally produced by specialized workshops or food companies. However, this does not mean that it is completely unnecessary for individuals to make it themselves. Because many workshops are produced in the form of family units, but they transition to enterprises or other forms as the scale of production expands.
And soy sauce replaced fish sauce a few centuries ago. This argument is limited. In Fujian, at least in the last century, shrimp sauce was once the most popular condiment in the local area, even more popular than the dynasties before the Qing Dynasty (if my studies go well, this will be the research topic of my doctoral degree).
And now it is difficult to say whether people have sufficient reasons to make their own (or family-made) fish sauce. I can give several possibilities: ① Families have the habit of making their own fish sauce. For example, at least half a century ago, Taiwanese families would retain the marinade (the original version of fish sauce) during the marinating process; ② When fish sauce is profitable (such as becoming a geographical indication or an Internet celebrity product), there will be family-made fish sauce trials (that is, some family workshops); ③ Overseas Fujian and Guangdong people will buy or make their own fish sauce out of nostalgia for the past or to increase family identity. (but I don’t have any relevant information about overseas Chinese making their own fish sauce. I only know that in the last century, most of the fish sauce factories in Southeast Asia were opened by Chinese, as can be seen in the local chronicles.)