This Others group has the endless source of strength in the form of new projects. STEEM and BTS have been in the group for a while but new players are getting added continuously, take EOS or Cardano. And many other cryptos with the cap higher than $100kk were created in the end of 2017 - they are also members of this group. New blockchains and dApps are getting created every day and some of them represent bigger interest for investors.
BTC itself has lost its dominance for me when I faced extremely high fees in Nov-Dec 2017. After this I completely forgot about BTC as a way of transfering value and I'm completely happy, cause except avoiding fees I started to enjoy the speed of transactions many cryptos are offering.

BTC tps is at the lowest level for the past 2 years (proof: https://blockchain.info/en/charts/n-transactions?timespan=2years ). My own explanation is that many people had to try other crypto during high fee season in BTC. They tried and they liked, now they do not want to go back :)