Because all Popovers are setup the same way: You press a keycommand, you enter your information, you press ENTER, it would make much more sense also to apply text changes via ENTER, not Ctrl+Enter.
I imagine it:
Enter → Apply Changes/Leave Text field
Shift+Enter or Ctrl+Enter or Alt+Enter → New Line
Or maybe even give as the option to toggle between these two setups.
I can’t imagine changing the default behaviour here, since I think it’s just too hard-wired that people expect to be able to create a carriage return with the Return key. But I’ll think about whether it makes sense to add an option for this in future.
For what it’s worth, one user’s experience with the text popover after 30 months of regular use: this one constantly throws me off as well. I’d love this option.
Same here. Most of the time, I only enter text with a single line and one get’s used to exit popovers with the Return key. Therefore I often end up with a line break, I didn’t want to have. I would prefer a behaviour similar to Excel e. g., where you have to press Alt + Return to get a line break inside a cell.
I also stumble across this from time to time. So an option would be really helpful for me, a user who is apparently resistant to learning … 
I feel exactly the same as Dan. I use this constantly, I use it in every project many times. No matter how often I use it, it will always feel counter-intuitive.
No doubt there will be times when a carriage return is desired, but the vast majority of text entries for me are single line. So for me the way things are designed now makes the occasional king over the habitual.
If we can’t get this changed, perhaps consecutive presses of the ENTER key could re-interpret the entry as “accept and close.” The first press would react with a carriage return, but a second on would undo that, accept the text and close the entry box.
Alt-Enter like Excel would behave consistently with lyrics and the space bar.
I’ve gotten somewhat paranoid about the Enter key after using an unfortunate number of chat programs and going NOOOO, I was not ready for that to send. If it were consistent between different software I could adapt to either form… Maybe that’s another argument for the excel model?
Alt- Enter seems like an excellent solution.
I agree with Dan. I get two lines too often for an active user as I am. There should be something to improve this 
Alt+Enter or Shift+Enter would be my preference. Most of the time I only need a single line of text; double rows are special cases, so a special command for that makes sense to me.
Thanks for the feedback, everybody. We’ll see about adding an option for this in a future version, then.