Desperation, greed, and plausible deniability:
This is more about story than about reason. It's a recapitulation of the classic Pandora's box scenario. Before Pandora had the chance to open the box, Epimetheus (who guarded the box) had a choice of accepting Pandora as the gift from the gods (who MADE Pandora for this reason, wanting to punish mankind for Epimetheus's brother Prometheus and the fire thing). Science is thus Pandora, and releasing the evils of the world is unleashing the monster.
If it was a government or scientists with ulterior or desperate motives, then sure. Think North Korea threatened with nuclear war. This thing might kill them all, but if it does, the world burns with them.
Or maybe they plan to kill it and study the body and stasis chamber. They're for-sure totally certain that the bunker-buster bomb they have will finish it off, then they can get all that alien tech.
Maybe they don't care if the thing gets loose. If they still have the tech afterwards, then the monster wandering around is CLEARLY not their fault, it got loose because (insert enemy here) went and deactivated the containment/stasis field in an act of sabotage.
You don't even need to tell us your plotline. We can all see it coming. Godzilla, Jurassic Park, Pandora. The scientist know these stories, too. Make them ignore the consequences for the gains, and they'll act. Or make them see the consequences and they'll try to stop it. Your choice.