You seem to have two different misconceptions.

Firstly, it was common for entire families to share a single bed up until the industrial age. Sex was not something that happened naturally in a bedroom because it was uncommon for people to have any degree of privacy, even in a bedroom.

Secondly, there is the misconception fostered by contemporary entertainment that couples in the industrialized world during the early to mid 20th century did not commonly share a bed. This is simply due to the extreme prudishness of television and movies, especially in the US, at the time. The reality was that since the era of the private bedroom the sharing of a single bed between couples has been common.

I'm confused - are you saying before a certain time period it was common that spouses only shared a bed when having sex?