I think they may be bred that way, i.e. will not grow after blooming
(though the red "petals" are leaves).

I remember one large poinsettia growing by the side of the road here,
next to an avocado grove. I don't think it got any water, and
the soil was not amended, but it was pruned, grew & bloomed every year.

That will be a goal for me this year.....grow a poinsettia successfully.

Cal,
Where you live, close to the poinsettia's native environment in Mexico, you have a much better chance of getting one to grow than many who try. I wish you luck.

I imagine that once a plant gets established, it could survive on benign neglect, as they do in the wild. I don't know anything about whether the commercial ones are bred to bloom, then die. There must be info on the www about this question.

I was reading something just the other day about what causes the top leaves of the poinsettia to turn color, but my brain is a sieve these days, and that explanation has already evaporated. The actual flowers are pretty strange. Have you ever taken a close look?

Elizabeth