Imagine that there passed an international law that illegalized the ownership of private cars, and enforce people to use only public transport.
This will be very strange law, it’s good for our environment and to reduce pollutions and reduce consume of oil energy, but in our frame of time it’s impossible to pass such a law. Maybe in the other frame of time in future owning private car will be illegal.
People who wrote religious books, they are constrained by their frame of time's view towards slavery; it’s as just like our view towards owning a car; so why bother.
Another issue is pork , at the frame time when first book was written, pork was not used as diet at that time at that place, there was no pig’s bones found that used as food in the places where the first writers lived, so it’s ok to make pork forbidden no one will complain.
Even worse the first book writer considered that his god is god for specific people in specific area. He is not god for everyone and everywhere, he admits that there exist other gods but his god is more powerful.
I do not blame the first writer he couldn’t predict the future, he didn’t imagine that his work will have such influence even in after more than 2600 years, he just wrote it to make some people don’t forget about their origins and united them in one idea.
but with absence of copyright and intellectual property you can imagine what will happen, he just started a snow ball.