RE India have been building Bullets for about as long as Royal Enfield existed in England, 1901 - 1971 vs . 1956 - 2021; 70 vs. 65 years. As has been pointed out, these are workingman machines, and I believe they survived because form followed function, like the scorpion or horseshoe crab. As long as you don't frag the crank, virtually every other engine or drivetrain maintenance operation can be carried out with the engine in the frame. Accessible, appropriate technology for the intended users.