Comma-separated values are old technology and pre-date personal computers by more than a decade: the IBM Fortran (level G) compiler under OS/360 supported them in 1967.
Comma-separated value lists are easier to type (for example into punched cards) than fixed-column-aligned data, and were less prone to producing incorrect results if a value was punched one column off from its intended location.
The comma separated list (CSL) is a data format originally known as comma-separated values (CSV) in the oldest days of simple computers. In the industry of personal computers (then more commonly known as “Home Computers”), the most common use was small businesses generating solicitations using boilerplate form letters and mailing lists.
Some early software applications, such as word processors, allowed a stream of “variable data” to be merged between two files: a form letter, and a CSL of names, addresses, and other data fields. Many applications still do, perhaps because tasks requiring human input (such as constructing a list) are natural and easy using comma delimiters. CSL/CSVs were also used for simple databases.
Comma separated lists were also widely used in the earliest pre-IBM PC era personal computers for tape storage backup and interchange of database information between machines of two different architectures. The plain-text character of CSV files keeps them valuable even today, especially in a global context, because they largely avoid incompatibilities such as byte-order, word size, and character sets; and because they are largely human-readable, making it far easier to deal with them in the absence of perfect documentation or communication.