Bitcoin is less volatile than the altcoins. Altcoins are highly volatile, which didn't get more attraction from large number of users. It is just used as a profit making token. Recently very few altcoins grow high and soon after this lot of bitcoin users moved to altcoins expecting profit and once again seeing the bitcoin price increasing started coming back.
Compare back then when bitcoins are not much distributed to different persons globally, this time is different and yes we can say that bitcoin today are less volatile. We can see and noticed that when there is an ongoing attempt to make the bitcoin price decrease. Somehow there are lots of times now that bitcoin withstand the deepest price low even the FUD was a major one.
Yes when there is a crazy movement on some of the alts, most traders taking advantage on it to make profit in the first place but it doesn't mean they will put their money in that coin for long term purposes. Still bitcoin is the one they preferred mostly in terms of long term investment. That's we called taking chances of every opportunity to earned a decent one.