A couple more points of necessary history...
So now the body was ready to store their stubborn spirits in. With the body's amped new ability, they basically could 'vacuum' those reluctant spirits back into bodies whether they wanted to come or not.
This is the species who ended their slavery by killing off the hybrid's father race, (which the hybrids didn't know for the longest time) and although they detested the way they were treated, they unfortunately picked up some bad habits on how to treat their work force obviously. Then, to prevent their folk from just lying down and dying again, they upped the human body's will to survive, too.
Since the only way to leave the 'car', was to die, this adaptation caused the occupant to be far less able to escape back into the spirit realm. Kinda like having a regular seat belt compared to one of those 5 point racing harnesses, but without any release.
There is a 'shelf life' on spirits--somewhere along the lines of 15-20 years out of a body, and the spirit will deteriorate to the point it has to return to a semi-sentient form and basically start over again, so the leadership was feeling some real pressure to get these 'holding' bodies up and running. I think they'd already permanently lost a good amount of their folk, which was quite worrisome because they had far less folks to lose.
Most species are far smaller than us because of the human body's ability to abduct any spirit, aliens as well, which has made us a very large species. The true population control is getting that abduction amping turned off. Which is the real reason NASA hasn't got us off this planet. The rest of the alien community don't want us anywhere near them, until we get what they consider to be a very nasty habit of stealing their spirits, shut off. So they've encouraged the hybrids to limit that program.
Anyway after the aliens successfully got some of their folk back in to a body that could get put back to work, they found the little now humans were soo sad because they weren't able to access the 'bliss' state which passes for sleep for that species.
We'd call it incapacitating grief/
Depression nowadays, but it caused the newly reincarnated folks to just sit around and cry, and still not work. The leaders were getting very frustrated--if they had hair, they'd be pulling it out---but finally figured out to shut down our ability to remember past lives, since if the folks couldn't remember the bliss state, they wouldn't miss it, even though they'd have to keep retraining them--a cost they thought worth it.
So we lost our easy access to that very important part of ourselves. And the aliens finally gained the work force they wanted. Although the newly reincarnated folk could feel something was missing--something important--they didn't know what, so much like us to this day, they just pushed it aside and went back to work.
The next issue they ran into was the aliens reincarnating into the human bodies too. They had different ideas and thoughts and started influencing their own little folk to be more independent and less obedient aka not wanting to work, just because a leader told them too. This whole process had almost a Cat in the Hat quality to it--fixing one thing kept messing up something else.
Since this species is really xenophobic, just the presence of others aliens around them, was enough to make them anxious. They hated that the other now human aliens were 'polluting' their little folk with these ideas. Since much of the information was shared telepathically, which is a much richer, far more immersive method of communication than just the spoken word, the leaders thought a way to stop that influence was to shut down our access to those natural telepathic abilities. And then kick the other alien types out of the compound. Problem solved.
But now they couldn't easily tell who was one of theirs and who wasn't. With telepathy, it had been easy--their little folk were very limited--other aliens much louder, bigger, so they devised a behavior test. They turned them loose in the compound and told them to have fun, but not to eat that fruit over there.
One of theirs would never eat the fruit. Any other species always did, so if anyone ate one of those fruit, out of the compound they went, where they couldn't influence the little folk. The aliens thought those other aliens would just wander around until they died, because if any of them were put out like that, they would. I'm not sure how they missed the fact that their amping of our will to live would cause those expelled aliens to find ways to survive, but that's a kind of typical example of how short sighted these aliens can be.
Anyway, more next time, cuz there are still more historical points that are important. Like I said--the hybrids have modified or made up soo much of what we believe to be history, including things like the garden of Eden stories to explain any lingering vague sense of the real history that we might have from the spirit level.