I dunno about that. My primary mountain bike is aluminum. It’s $2,000 for the frame alone. Aluminum is vastly underrated in today’s carbon world. The axiom still holds true through: Even with aluminum, you can have any two of strong, light and cheap.
You can always find an expensive version, but my point holds. Basic cheap aluminum tubing is strong enough and light enough for most basic biking needs in poor countries. You CAN have all three, just not to extremes. The center of the triangle exists.
my D’Adachi Steel Pinarello road bike wasnt cheep, but its very light and strong, the weight of most aluminium but with more flex giving it a very smooth ride, its over 10 years old now but still a great ride! now for alternatives to metal, a buddy of mine makes bamboo bikes, no welds, uses twin and resin, he rides them all year round even in Minnesota winters, he does use metal forks and hubs