What really makes Androids lack empathy?

Rachael Rosen is so far known as a sophisticated and well-designed Android, and her personal essence changed subtly but deeply after her realization of her true identity.
Rachael Rosen first shows up in Chapter Four as the niece of Eldon Rosen, the boss of the Rosen Association. In the beginning, she was characterized as an extremely professional girl who works in Rosen Association. Whereas, after Rick did Voigt-Kampf test on her in Chapter Five, she was determined by Rick as an Android. To avoid being recognized by Rick, Rachael Rosen was cautious when answering her questions. Though she asked about every detail before answering Rick’s questions, she still got recognized due to her short pause before her propriety reaction in her final question. After Rachael found out that she was an Android, realized that her memory was planted by Rosen Association, and figured out that she wasn’t supposed to be on Earth technically, Rachael’s attitude changed. Instead of escaping from Rick, she offered help to “retire” Androids with Rick voluntarily, probably aimed to avoid being “retired” before Rick’s other targets.
Rachael’s essence changed at the moment when her identity was brought into the light by Rick. Before that moment, Rachael knew that she was an Android and everything she did was to avoid being caught. Her goal was simple and pure: to maintain her fake cover as a human, and her enemy and allies were clear: Rick was her enemy and Rosen Association was her shelter and she would do anything it takes. However, after she was identified as an Android, her essence became twisted and she began to play on both sides. On one hand, she still wanted to maintain her cover as an Android and had back up from Rosen Association, so she didn’t even have the idea to escape from the Rosen Association and began her tramp like most Androids who escaped from the Mars to the Earth did. On the other hand, she wanted Rick as the second guarantee of her life, thus, she offered help to Rick to retire other Androids. Since she knew that she was an Android, she immediately gave up her empathy. In her opinion, it was beneficial to exchange other Androids’ “life” for her safety.
In this book, the author makes a setting that Androids don’t have empathy. However, Rachael, being an Android all the time, showed her likeliness of having empathy first, but she gave up her empathy later. Thus, it’s arguable that whether the identity of Androids made them lack empathy or the acknowledgment of being Androids made them give up the opportunity to chase for their ability to have empathy.

I fully agree with the idea that Rachael has witnessed a huge change in her personality and attitude towards empathy after she has been tested out as an android. That lead her to play on both sides. But I doubt the extrapolation Elaine has proposed that Rachael actually knew that she was an android all the time(before the test is being given). First evidence that disagree with Elaine's claim is the book's description of Nexus-6. The book clearly pint out that Nexus-6 is an highly developed type of android that get their memories implanted before they even have consciousness. If they woke up and find themselves being alive and have past memory, and they found they function and integrate exactly like human. They are not likely to know that they are intrinsically fake humans. Secondly, it seems more reasonable for Rachael to have such a big change if she doesn't know her real identity, rather than always knowing it, right?

I agree that Rachel's essence has shifted after she discovered the fact that she's not a human. Yet I am not sure if her essence is now totally for survival, since she shouldn't have risked calling Rick, a bounty hunter, if she simply wants to survive. It's quite possible that Rachel is now trying to convince herself that she's a human and to repress the fact that she's a human in order to avoid anxiety. Perhaps the best way of convincing herself that she's a human is to do what humans would do----retiring androids, which explains why she would offer to help Rick terminate androids. However, I also believe that her essence of "trying to become human by killing androids" are quite fragile since such essence would cease to exist as long as someone tells her that she would never actually be a human without empathy, and her life would again be pointless. Thus, I believe that Rachel's true essence is more of a lie to herself or an attempt to defend herself from the unacceptable truth.