Probably accessibility reasons. Even ancient browsers or obscure browsers support text. Their is a non zero chance a browser wouldn't support the image format,

Probably accessibility reasons. Even ancient browsers or obscure browsers support text. Their is a non zero chance a browser wouldn't support the image format, or the image might not scale across different screen sizes. Also iirc their was some vulnerability that used a image format so that's also a issue to think about. Finally, text makes web scraping/parsing much easier, and even ignoring that text is smaller than any image format.