Because as shown in the dialog, your image is 2 inches if you print it at 1374PPI. The figure you give hints that it is printed at 600DPI which could be the maximum that your print driver allows.
If you want the image to be 2" high at 600DPI, then scale it to 1200 pixels high.
Another solution is to export the image, open a word processor, insert the image and set its dimensions in the word processor, and print the page from the word processor.
PS: with text, it is normally a good idea to work at the right size for the start, the 30px font isn't exactly a half-size 60px font, smaller fonts have subtle changes to improve readability. Since Gimp is a bitmap editor, this kind of information is lost and when text is scaled down (later in Gimp or in the print driver) your small print is less legible.