It was the cheapest basegame sink so I guess Simstar's explanation is correct.
Anything that breaks a lot will get the option to be replaced at some point. Sinks, tv's, computers, showers, etc. If you go ahead and fix it, there's no disadvantage other than it's more likely to break again. If you repair it with a sim who has completed the appropriate handiness challenge, however, it will never break but that option will still be there.
If it's upgraded and you replace it, you have to upgrade it again.