Considering there are thousands of coins and tokens out there, what sort of dominance should Bitcoin have which shows that even though it remains the dominant force there is still a lot of space for others to narrow the gap? Currently the BTC Dominance according to CMC is: 62.6%
After all, bitcoin is bitcoin! 
Everyone prefer bitcoin than altcoin as because Bitcoin already have gained trust. People belive "Bitcoin price may go down but it is not scam". I think this is the main reason behind BTC Dominance with large number of share/percentage. Top10 coin/token in CMC may increase by theirs Dominance after bitcoin