The coin is issued by a central entity who has kept 50% of it. This makes people suspicious. Bitcoin has no central issuing entity, thus no one person to 'get rich quick' in some scam type operation.
Bitcoin itself is less of a pyramid scheme than gold. This is because even when the price stops to rise (or even when it collapses) you can use it to easily transfer value across the world.
I won't, ever, be buying bitcoins for this and other reasons.