I don't think Bitcoin is losing its appeal and popularity if compared to other altcoins...indeed it is still holding the higher volumes of the whole crypto market..
Of course investors are realising that putting money in the right altcoin at the right moment can give you more profits than Bitcoin...but this depends a lot on the moments you invest...for instance between October and early December Bitcoin has been growing more than any other coin...and this cycle might repeat again in the very next future