Short answer: Poinsettas are potentially long living perennials. Most christmas ones die off shortly aftwerwards due to a combination of ignorance and neglect: Fact 1: most christmas poinsettas will be shipped in the smallest pot possible, leaving no roof for growth and making them top heavy and prone to tipping. Fact 2: Many people will overwater or underwater their houseplants. this is exacerbated if a plant is kept in a too-small pot. Fact 3: The vivid red leaves of the plant are caused by deliberate light deprivation done weeks before sale. Left in ordinary light, the red leaves will fade, die and drop off, though the plant is still alive. This will lead some people to think it is dead and throw it out.
To keep your pointsetta alive, make sure it is in an adequate sized pot, its soil is kept moist but not too wet, put it in a part shade envioronment and be prepared for it to morph into a boring, green bush.