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.
Manipulation 101Not COMPLETELY true because the price of altcoin could be VERY LOW.
Of course there are lots of alts.
But what's interesting is that they have not a void price at all.