The problem is that visa policy is so complex, unless you rely on an authoritative source like TIMATIC it's not going to be right, and that's going to cause people to not book trips they would have -- or worse, book, expecting to go, and have to cancel.
For instance, China. It says that for US citizens a visa is required. That's half true.
* There's TWOV (transit without visa)
* Transit Visa On Arrival where if you're connecting to a third country within 24-144 hours depending which city you're visiting you can get a transit visa when you get there that entitles you to visit just the city in which you landed but not leave. [1]
* Hainan has a 30-day visa waiver program if you apply through a travel agency. [2]
* Hainan has a 30-day visa on arrival program. [2]
* Hong Kong and Macau are 90 days visa on arrival.
In this kind of international diplomatic space, accuracy matters more than anything else.
[1] https://www.travelchinaguide.com/embassy/visa/free-72hour/
[2] https://www.travelchinaguide.com/cityguides/hainan/visa-free...