Tessa was desperate, and a two year contract with an Imperial Embassy looked like the way out. Helping a newly contacted species develop to a point where they're ready to deal with the universe is a years' long project, and those whose missions succeed can expect more lucrative contracts in the future as well as the knowledge they've helped an entire species survive.
The Empire of Humanity is not being altruistic. It has selfish reason to want the Morelli and others to survive. But the Morelli must be willing to learn, and there's only so much latitude a species may be given before even the Empire's own citizens require suppression or worse. Tessa and her superiors must find a way to persuade the Morelli to learn about the dangerous universe beyond their current holdings before the Morelli do anything irreversible.
Because evolution is not done when a species achieves sentience, or even technology. It becomes communal, and the penalty for failure is extinction.