I'm pretty sure it's because of unit bias, whereas the new people are thinking like:
"Bitcoin is at $17,000, it's quite expensive; whereas Cardano is only at around $1. $10 soon! To the moon!"
Something like that, not taking in to account that most coin's circulating supply is too high to reach high dollar prices.
I was actually just reading an article like this, where people get too consumed with the price itself and fail to look at PERCENTAGE gains -- which are of course everything when it comes to investing.
But yes, people now think that because all of these new alts are hitting the top 10 and are overtaking one another (all while increasing in alts market cap) But most of the coins that are new in the top 10 have NO ACTUAL USAGE - Tron, XRP, etc.
Bitcoin is the only thing here that matters, you MUST remember that.