By default, all text gets added at a size appropriate to the drawing's current zoom level. However when you want to export your work, the various text sizes may not be 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.