But it's been already a couple of days that the dump initiated and dominance hasn't change.
In the past, it used to change as the dump starts
Get to know how dominance is calculated first and you will have a better clue why it has not changed much.
BTC Dominance (%) = (Bitcoin Market Capitalization / Total Market Capitalization) * 100
Now, you have to understand that money left the whole market and not just bitcoin. We saw every other coin moved accordingly as their value decreased, so in a way, when it comes to dominance, nothing has changed.
You will get to figure that out the more this way; if money is leaving altcoins into bitcoin which pretty much will show you a bullish bitcoin and bearish altcoins, BTC dominance increases and it happens the other way round as well.