That is not happening to all alts. Some are taking some really good pumps, as you can see if you look to bcash. To be honest I don't really understand that pump. Maybe since the BTC price is increasing so much, and there is an upcoming fork that is kind of an attack to bitcoin, they are trying to send the message that bcash is still an alternative if anything goes wrong. Of course that everything should go well, and BTC will just come out stronger as usual, since it keeps proving us that it handles well this type of stress. So yes, maybe you are right. As investors see that bitcoin is a solid coin, they might start to focus their investments on it, instead of risking their money on alts that probably won't do as well as BTC to these kind of tests.