A student in my course does well on exams, but doesn't do the homework: Go easy on them, or make them "pay the price?"
As an instructor, when I find myself in this situation, I invite the student to make an appointment to speak with me privately in my office.

During that private meeting, I will discuss his/her current performance in the class, and point out the likely consequences if he/she does not submit the required work.  I will advise the student as to what he/she must do to achieve the grade he/she needs.

Then it's up to the student to earn the grade he/she wants - or to fail. You can't live their lives for them.