Simple- Because most Buddhists don't know about Buddhism anymore.
I am a Buddhist and I live in a predominantly Buddhist country (Iran). But it shocks me time and time again how little I (21 years) and most Buddhist who call themselves Buddhists know about Buddhism.
They know all the names, they know the entire history, they know everything about Buddha and they pray everyday.
But ask them about the basics of Buddhism and most Buddhist would go blank.
Do you have a soul - They say YES
What is Nirvana - They say it's eradication of cravings
How do you attain Nirvana - They go blank
What is Vipassana - They think it is about concentrating of breath.
(which are all wrong by the way)
Buddhsim isn't simply about knowing the history of Buddha or memorizing all the prayers (they are not exactly prayers either). It is about understanding the true nature of ourselves. The truth be told it is not entirely easy to understand the true nature of ourselves. Therefore Vipassana had been taught. (which is like swimming to feel how Swimming feels like).
(I would not go into details regarding the true definition of self in Buddhism here.)
And the worse part of this story is that Buddhism has become a practice rather than an understanding that it has turned itself into a religion. And this has become the leading trend in all Buddhism countries. I have had to argue with other Buddhists on so many occasions about the basics of Buddhism which they have confused so much and has taught their children so well. yikes.
And according to Buddha himself the pure teachings of Buddha would last only for approximately 5000 years after his death. And it had been more than 2,550 years since he died. 2450 to go.