It's not that they can't have, it's about they will not. Because it's a kdrama with universal viewership, they(director, producer...) take lots of things in consideration (FL's age will be one such parameter). And it's my opinion, it differs with every individual.
ML should get out out of this loop. This is seriously frustrating now. He should take a leave or transfer himself and go to beach side areas to clear his head. wtf is wrong with this show, it keeps coming in circles.
Why this show is so underrated? This is one of the best kdramas i have ever seen. Totally changed my perception of kdramas. It should be rated higher tha 9 in Mdl atleast.
The tragedy with ML and FL is not as big as they shown in thedrama with overdramatic expressions and dialogues. The story lack depth all in all. But you can watch it for Main lead and Second leads chemistry which is good through out the show. Anyway You can digest most of the things at first watch.
Loved the ending. All goes well if it ends well. 10/10. If only writers of reborn rich and 2521 knows how to end the series, those series had becomes 100 times more rewatchable.
K-Drama 
And it's my opinion, it differs with every individual.
I m just not in a mood to write a long paragraph here. So leave it.
wtf is wrong with this show, it keeps coming in circles.
But you can watch it for Main lead and Second leads chemistry which is good through out the show.
Anyway You can digest most of the things at first watch.
If only writers of reborn rich and 2521 knows how to end the series, those series had becomes 100 times more rewatchable.