While working on a drawing, text gets added at a size appropriate for the drawings current zoom level. However when you want to export your work, the various text sizes are not ideal for a final presentation.
There are two ways to "fix" this issue.
Solution #1 - Set the text size to never change
Solution #2 - Once you are ready to send out / show your work - change all at once.
The video below shows how to select all text and make them all a single appropriate size.