OP, as others note in many ways here, you should not expect them to behave differently because you're pregnant. Hoping that a baby would make them more interested in you is putting far too much of a burden on the baby, frankly. They did not give you the attention you wanted before you were pregnant, so why did you believe that your pregnancy would change them? You cannot control other people; you can only control your reactions to other people. Your hurt started way earlier than this pregnancy, clearly.
One other thing: They may be from a generation, region of the country or culture where it's just not considered the "done thing" to lavish attention on others -- yes, even on their own adult children -- and they may be from a place or time when privacy was the norm, especially for pregnancies. I'm not saying they're medieval here; but I know my mom was a very loving but very private person who believed that others should have their privacy as well. She and I kept in good touch during my pregnancy -- but we were very close and had always stayed in close touch before I was ever pregnant. But she did not rush up here to see my pregnant self, and she said to me clearly that she would not come up for the baby's birth but would come some weeks afterward, so we would have time to adjust as a family. That was all perfectly fine and what I would have wanted (and what I would have expected of her, based on her lifelong personality, which my pregnancy did not change for her). Base your expectations on your parents' long-proven actions and their values (such as valuing privacy, or valuing their own time now that they are empty nesters, perhaps), and not on your hopes.
Have you tried just asking them to come see you? Just saying out loud, "I really want you be more involved in my baby's life and to call me more often now than you have in the past?" Why not say it? They may have zero idea that you want that and may say "We thought you'd want to be alone with your husband/enjoying being pregnant/there's nothing we could do to help/we don't want to be in your way...." Those are the ways many older people think. "We don't want to be in the way." But you're interpreting it as a slight against you when it may be their attempt to give you what they think you want - they won't know otherwise if you have not told them otherwise.