Well, it is same for everything.
Why get a 15k+ harley davidson when a vespa only cost around
1k?
Why get an integra when a honda civic is much much cheaper?
Why get a 5k gibson SG when a vantage cost less than $300?
Why get a 10k grand piano when a half set keyboard cost less than
$500?
The same theory applies for everything above. Its all about the
performance, quality, brand, etc etc. I believe commoners can
easily understand the concept behind all these price
differences.
It is the same for bicycles, just because we always see those
market bikes around which cost less than $150 or even 'high-end'
market bikes that cost about $250, most people have the concept
that bicycles are supposed to be around that price range. But when
one commit itself into the sport, a decent MTB can easily cost 3k
while a decent roadie can easily hit 5k.