Nothing changed with the bats. Antibodies to bat coronavirus were found in humans in villages near the bats’ caves years before COVID-19 showed up. (IIRC, there was a link on FR to this a couple weeks ago.) In the same study the researchers found 500(!) different coronaviruses in the bats, and thought they had only scratched the surface.(!!)
What changed is, primarily, travel and the transportation system in China. Compare maps of the road and rail system in China 30 or 40 years ago, vs. today. The transformation is nothing short of astounding.
Plus, the bulk of the population was lifted out of abject poverty, so they have some money to travel - mostly by rail or bus. And, do they ever. I saw an estimate of 15 BILLION person-trips (intercity, national, international, etc.) expected for the 2020 CNY, before all this (virus) hit and the lockdowns were imposed. From some personal connections / knowledge, I don’t doubt that figure at all.
In the past, if a virus made the jump, most likely it never made it out of whichever village or region near the cave was afflicted. That’s not to say there were no epidemics - there have been great epidemics during cold spells in China’s history, and probably many lesser ones lost in that long history. But the ones we do know of were, as you imply, less frequent. (Side note: COVID-19 would likely have not even been noticed in China before, oh, I don’t know. Maybe 1900? People, especially elders, got sick and died routinely from all sorts of causes of pneumonia. Some years more than others. Only particularly nasty epidemics with high fatality rates would even get recorded, I suspect.)
Now, you have all this unprecedented travel, which includes, by the way, substantial tourist traffic to the caves. (Some of the caves are dang impressive - I’d go see ‘em too, if they were within a day’s drive from me.) However, Chinese culinary, hygiene, and animal processing and slaughter habits have not caught up to the new realities...
I did a little post on a separate thread but I’ll bring it over here because it has the links to what you’re referring to. Note also, there are primates in the same area. And that 12 residents of Kunming were some of the first confirmed cases of Covid and a thousand cases came from the area.
Repost of http://www.freerepublic.com/focus/news/3820124/posts?page=53#53
what if it wasn’t Wuhan out, but Wuhan in? Brought into Wuhan, from an infected cave tourist or even an infected vendor of flowers ?
“Vegetable growers from Sichuan and Guizhou provinces are predominant in Kunming’s vegetable markets, but the local people are quite happy that it should be so. As a vegetable or fruit vendor from Sichuan can rapidly make enough money to buy a house and settle in Kunming...— fresh vegetables are available all year round in Kunming. The same also applies to fresh flowers. Flower growers in Kunming most like the autumn and winter seasons, as this is when no flowers grow in the majority of other cities in China. They consequently wholesale large quantities of flowers to big cities in other provinces...
http://www.chinadiscover.net/yunnan-tourism/yunnan-kunming.htm
“the team drew samples from people who lived near the bat caves and found that three percent of them had developed antibodies to the viruses - proving that the strains can and have infected humans in the past.”
https://nationalpost.com/news/world/cave-full-of-bats-in-china-identified-as-source-of-virus-almost-identical-to-the-one-killing-hundreds-today
At time of writing (Tue. Jan 28 19:40) ...In Yunnan there are 44 cases confirmed, from which 12 in Kunming. Most are people who came from Wuhan during January
http://wondersofyunnan.com/blog/posts/coronavirus
With 954 coronavirus patients, the province of Zhejiang is the hardest hit region outside Hubei
https://www.scmp.com/news/china/society/article/3049298/coronavirus-zhejiang-adopts-draconian-quarantine-measures-fight
http://wondersofyunnan.com/destinations/yunnan/popular-attractions/jiuxiang-caves-scenic-area-kunming
Caverns & Caves in Hangzhou
https://www.tripadvisor.com/Attractions-g298559-Activities-c57-t54-Hangzhou_Zhejiang.html
primates:
http://wondersofyunnan.com/tours/2-days-yunnan-snub-nosed-monkey-tour
And that increased travel also coincided with increased capability to modify viruses. Just a coincidence, no doubt. Or perhaps an unfortunate positive feedback.