Definitely altcoins are not getting boycotted. I was asking myself why is the price of only BTC and ETH are skyrocketing at the expense of other altcoins. Then it was done on me that investors are actually selling other altcoins they have gotten in order to buy either BTC or ETH, that's probable reasons why the price of other altcoins are dropping.
The reason you gave is indeed right, but there is one more possibility that makes sense in my opinion, investors are selling other Altcoins because they are still interested in Bitcoin and ETH, anyways it's also a very logical and natural thing because BTC and ETH have always been also has a lot of demand.