Some people don't have the time (literally) to start a new character when so much of said time has already been invested in one playthrough.
Going to college leaves me little time either.
Instead of investing all of that time into one overleveled character that I knew i would get bored with anyways I did the same thing I have always done in elder scrolls: divide my time across multiple characters specializing in different skills.
If i want to play an archer one night then I use my sneaky character. A mage? Use my magic character. Bashing things with metal? My warrior.
If you assume I have multiple characters because I have a rediculous amount of free time you are wrong. I simply plan out my playthroughs ahead.
Starting new characters isnt a question of time, its planning.
You are not wasting time by startig a new character, you are investing in a better second playthrough.