This is majorly because bitcoin still have the highest, over 40 percent of the entire crypto market capitalization dominance, which means bitcoin still controls the entire market in some ways, as ether goes up, bitcoin is also going up, ether has a higher chance of flipping bitcoin if bitcoin's market dominance comes down to atleast 20 percent.
Like you said the chances of Ethereum to flip Bitcoin are very low, especially with Bitcoin still dominating the market, it is almost impossible for
Ethereum to flip Bitcoin. But anything can happens, of course the Ethereum holders will benefit if Ethereum manages to flip Bitcoin,
but in my personal opinion it is impossible, even in the long term. I feel Bitcoin is too strong to beat, even besides Ethereum there have been
many other projects that were created to beat Bitcoin, but none of the projects beat Bitcoin. After all, Bitcoin dominates the market for more than
a decade, it has proven how Bitcoin is indeed very strong and has always been the number one choice for most investors.