Reasons behind ‘lying in’?

Can anyone explain the reasons behind the super strict rules for lying in? It seems like such a restrictive and miserable thing to undergo but I assume there must've been reasons that made it worth it to them.

Specifically, I'm especially curious about the logic behind not allowing the expecting mother to leave the room, get any fresh air or sunlight, and why not even the father would've been allowed in the entire time. Did they believe there were benefits to the mother and baby or was it moreso due to social/religious expectations like childbirth being a woman's domain?