When a person is dying, they are retreating from everything outside of themselves. They have little energy for anything outside of what is going on in their internal world.
They cannot respond the same to conversations as they once did. It takes much more effort to answer questions and to engage someone in the normal back and forth conversational style can be overwhelming for them. Instead, tell them a story. Talk about what you did today or whatever is on your mind. But don’t ask questions. What they have energy to share, they will. Do not be concerned if they do not respond to you the way they used to as it is not about you. Just keep talking to them if you want to verbally connect. Otherwise, your presence is enough.