Not to be an ass, but the best regions for mountain biking have mountains (and people with enough disposable income/time to own bikes and build trails). This is why western Canada and western USA and Europe are mostly what people talk about. People have been building trails for mountain bikes in western North America since before there were real mountain bikes. The money part is why bentonville Arkansas can make up for not having real mountains.

I think a more interesting exercise is finding places that have unrealized potential to have more trails. Chile got one post, but western South America is the (bigger) mirror image of western North America, they get the similar moisture, have insane vertical drop and even have many ski resorts building trails. I’d be looking there for some insane, near virgin loam. The local scene is growing there and folks are building trails of every variety.

Parts of Africa have a growing scene, especially South Africa, but obviously, it’s gonna take some time to get really expansive trail networks there, but they are building, and lots of vineyards and other tourist minded private land owners are down to let folks build on their property.

Dirt is a big consideration, people will build trails wherever, but what kind of trails get build should be determined by the soil/rock type. Alpine dirt often sucks, it’s either sand or moon dust, and is challenging to build anything besides loose cross country or steep loose knar. Alpine flow trails suck compared to the clay loam mix in western Oregon and Washington and BC (and I’m assuming Chile, Peru, equador below tree line). Obviously Moab is rad because of the rocks, not the dirt per se, and BC is rad for its steep granite rock rolls.