Since the dump from 6500$ (and actually since sept.) btc dominance has been very stable, around 53%.
However it appears previous bear market phases always had an impact on the indicator.
BTC dominance has been pretty much on that level for a while now. The dump is nothing considering the fact that it was something that hit the whole market generally and not just bitcoin. It was not like bitcoin was dropping and the altcoin market was rising. Bear market as we have all seen it is something that affects the whole market overall when it hits, what we are seeing now is just the statistics based on the market cap over all compared to the rest of the market and the dominance of bitcoin totally depends as well on the sentiments of the market overall and where money is moving into.
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
Maybe you should be reading more on how that dominance is calculated and probably you will figure out the main reason why it has not changed. Bitcoin was not the only coin that dropped, the whole market did, and the dominance of bitcoin is compared generally with the whole market, and the reason why you see the dominance not changing is because money is being moved out from all markets generally, and the percentage of bitcoin in market cap to the total altcoin market cap, simply gives you what the dominance is all about.