Why does my exports say .jpg

You don't need to change anything. Both extensions can be used and I don't think there is any application that would not recognise the .jpg extension for JPEG files.

".jpg" is the most commonly used file extension for "JPEG" files, which Lightroom and probably most other image-editing programs typically use when creating such files. Lightroom will recognise files with the extension ".jpeg", though its export process will always create the ouput file with the ".jpg" extension. Same goes for "TIFF" files, the usual extension would be ".tif".