While tuberculosis was common, it takes years for someone to die from it. Those three diseases can kill people within a week, so they were common causes of death on the road. Trail caravans were just lots of people huddled up for long journeys that didn't wash their hands... think about it.

*Turns into a food dispenser*

The main obsession is fully dynamic lighting, which is pointless when you have a lot of static shadows that won't ever move, so it eats up performance. The less performance you have though, the more likely you will buy a new GPU. It's not about graphics anymore, it's about selling new hardware.