It just means that people are getting smarter to invest in Bitcoin rather than spend their money in other useless project. If it were to continue, we might see some increase in BTC price in the next months. The only one I deem worthy is ETH and Monero as an alternative to Bitcoin.
If Bitcoin where to increase more in Volume, more and more altcoins gets shut down.
Most altcoins does deeper because they are meant to be independent and since they are not active enough to convince investor to put money into their own market, investors will continue to follow the hype and usefulness of bitcoin, and that is why you will see that bitcoin is increasing more in dominance than other altcoins.
I know that altcoins seasons too will surely come, but the majority of the altcoins if care is not taken would have already lost all their pride and lost all their customer to bitcoin, if they are not even lost finally themselves, but i trust more in those coins that are at the top market in either exchanges or the top in the most popular ranking site of coinmarketcap, then bitcoin dominance would have reduced a little bit or remain constant for a while.