I think both charectors are supposed to be workaholics, people that lose themselves in their job and basically spurn family dynamics. Miles has engineering and Keiko was a botanist.

I think the writers wanted there to be that “we are both focused on our work and not each other” dynamic to their relationship, and wanted Keiko to be frustrated as a workaholic denied, being pushed into both the family role by their daughter and having no plant life to study on DS9.

The “become a teacher” was a sublimation that worked for a while for her, but that of course fell apart.

The other hand of it to is that theirs is one of the few relationships where you can feel the strain of competing needs on trek. Most relationship issues are pretty low stakes, even the ones played up like worf/jadeza wedding. Like, it is all going to be wrapped in a tidy bow and we know it.

Miles and Kieko were both driven people, and Kieko was being stalled out and was frustrated by it. There was no easy answer, just like the real world. Sometimes relationships, even otherwise healthy ones, have issues. Both actors were able to show them well, so they leaned into it. Unfortunately, it makes for unlikely people at times.