these guys understand it
Bitcoin's share of the total marketcap (not its dominance) is decreasing because of a very simple math.
market capitalization = supply * price
increase the supply you increase the marketcap.
increase the supply to a ridiculous number like 100 billion you get a ridiculously big marketcap.
now have hundreds of altcoins with ridiculous numbers you get a huge total marketcap in which bitcoin has a tiny share.
Good thing that no one cares. There are hundreds of completely worthless alts with market caps of >$1,000,000 even if their trading volume is just a few thousand. All it takes is a meaninglessly large supply.
in short make an alt with 5trillion coins premined.. put ONE.. yes ONE coin on an exchange and sell it to yourself for $1.. yes spend just $1.. and BAM market cap of that coin is $5trillion
market caps are a MEANINGLESS number. its a bubble number backed by nothing.
there is not $5trilling backing the premined coins i used in my example. just like there are not $28+billion in bank accounts backing bitcoins market cap. nor any other altcoin.
the sooner people realise this and stop giving a crap about market cap, the better.
here are things people SHOULD care about:
how many merchants accept coin X
how many employee's are working to do something within a certain coin, (devs, consultants/trainers, convention organisers, device(HWwallet/asic,etc) manufacturing employees, payment processors/exchanges etc, etc)
how many users a coin has
though some of these details are not easy to find. they are a hell of a lot more important stat than market cap