Pro-Choice?? really...

Why does it seem as if many that are on the 'pro-choice' movement aren't really for 'choice' at all if it means that you 'choose' to birth the child that is in the womb?? I mean, there were groups that really got mad that CBS decided to air the ad where Tim Tebow's mother testified that she decided to 'keep' Tim before he was born. That was a choice....a choice to keep. Why can't 'pro-choice' be equated to CHOSE TO KEEP A CHILD & BIRTH HIM INTO THE WORLD??