The reason is that so many of the content creators constantly power down. Really who can blame them? The sell Steem/Hive and buy BTC trade has been working for years. I have long said there must be a reason to stake Hive apart from some inflation reward and being able to vote more for other content creators! Thankfully we are now free from Steemit's constant selling. Even so with more Hive being minted daily, will we ever have so many users that will power up enough of the liquid supply in order to let the price rise?
STEEM went from 7 cents to $8.5 in just ten months. That's 124x despite the 8.5% annual inflation. Even if all the newly minted coins hit the market immediately, it would be nothing compared to the immense volatility of the coin price.
When it comes to the scarcity of BTC as the source of it's value, we should not forget that it's also the trust in the permanence of that scarcity that gives it value. Bitcoin is decentralized and does not have a governance structure. It's a PoW coin and it's harder for stakeholders to make a stupid decision together.
By the way, I'm all for ads on Hive front ends. They could use the money on development costs or they could partially share them with their users by issuing tokens redeemable with the money earned from the ads.