It is probably, and often, tied to the evolution of Christianity and Western humanism that led to a special view on the rights of the individual. Which for instance led to the abolition of slavery in the 19th century. Which to us is baffling someone even ever though slavery was ok. Yet it was the standard for millennia.
When you read a summary of the Buddhist doctrine this Western view of individuality seems to fit perfect. Yet the cultures housing buddhism didn't yet seem to have evolved to support this view of the individual.
This might have something to do with the fact Buddhism started in a more complex society in India and then moved to more tribal places like Tibet. Yes India had a feudal type of cast system, but also had a very high level of philosophy.
This is an argument that's also sometimes made by scholars to explain certain differences between the word of Jesus and the more tribal verses of Mohammed.
Coming back to Tibet, even though it was far from perfect, there a still gems to be found in Tibetan Buddhism.
And to give them some credit there have definitely been attempts to reform in Tibet. Not every monastery was about politics, some teachers created their monasteries far away in hard to reach places to avoid the politics. For centuries the Tibetan writers already speak of dark times, so at least a few were aware.