Why do some mothers from the sub continent spent the first 40 days after child birth at their mother's place?

**Why do some mothers from the sub continent spent the first 40 days after child birth at their mother's place?** I was also told they are allowed to miss their prayers and fasts because of 'Nifaas' - post‑natal bleeding. But from what I understand, the Nifaas among women is not a universal standard. Some are free from it earlier than others. Also any blood beyond 40 days isn't considered from Nifaas. Hence, please clarify on the 40 day ritual and is it a bid'ah being practiced in the name of keeping wives and new borns aways from their husbands to avoid physical interactions. **Was it a practice among the Sahaba?**