Of course you're correct that these also had higher, and probably much higher, mortality rates. But what matters is overall impact. Let's say that x% fewer people die in childbirth today. What would that mean? What you'd start by doing is seeing the cause of death for a large sample of people in times past. So let's say you look at 100,000 people. How many would have had mortality caused by childbirth? It'd be extremely negligible and almost certainly in the single digits if not fractional. Keep in mind you're looking at all deaths, not just deaths of women who gave birth. And so that x% improvement results in a comparably small gain - childbirth being safer does not have a major quantitative impact because its rate as a general killer was, and is, very low.
What would be killing people? All the way up until the mid 20th century famine was one of the biggest causes of death. Famine and related issues all the way up until the mid 20th century was a huge killer. For instance in the early 1900s around 27 million people died in famines with a world population of about 1.7 billion. [1] That's 1.6% of the entire world dying of famine in one year! Now go back 3000 years with all the difficulties that entails.
And then consider things like food poisoning. We consider it, as a cause of mortality, mostly eradicated in the developed world. Yet it was such a pernicious killer that "eradicated" translates to 3,000 deaths from foodborn disease per year in the United States alone [2]. And now once again, go backwards in time to imagine how radically worse things would have been. To give that number some contrast consider measels. The vaccination was introduced in 1963. In the decade leading up to the immunization 400-500 died per year from it. [3] In other words foodborn disease is a bigger killer today than measels was before there was a vaccination for it. This isn't some anti-vax thing, but trying to give perspective to how and why people have died throughout the ages.
[1] - http://www.thegwpf.com/the-era-of-great-famines-is-over/
[2] - https://www.cdc.gov/foodborneburden/index.html
[3] - https://www.cdc.gov/measles/about/history.html