In the past, there were two popular methods of encoding 8-bit data as human-readable ASCII: uuencode and Base64. Uuencode was widely used in USENET ‘binaries’ groups and was known for its robustness and user-friendliness. However, it was sensitive to line breaks and formatting, and some people didn’t have decoders for base64-encoded binaries. Eventually, Base64 became more dominant, especially after MIME (Multipurpose Internet Mail Extensions) adopted it as one of its supported encodings. Base64 was considered more resistant and compact than uuencode. One reason for the shift to Base64 was the rise of graphical email clients and web browsers, which made it more convenient to handle binary file transfer. Furthermore, Base64’s usage in URLs also contributed to its popularity. Overall, the decline of uuencode was influenced by factors such as compatibility issues, convenience, and technological advancements.
https://retrocomputing.stackexchange.com/questions/3019/why-did-base64-win-against-uuencode