It's most likely the latter. Most Whales are moving bulk of their cryptocurrency investments to Bitcoin and maybe to one or few established Altcoins. Most coins aren't living up to expectations and investors are losing interest.
It's also possible that investors are no longer able to buy the coins easily due to new regulations
The main reason for the outflow of money from alternative coins is a high level of mistrust. But with Bitcoin, everything is different, for everyone it is digital gold and even if you invest in cryptocurrency, then you need to buy Bitcoin. So many people think, so many do and its really good. It is necessary to clear the market, to kill several alternative coins that do not represent any real value.