Because paid shills on twitter only care about shilling centralized ponzis,
And elon think the entire cryptocurrency market is joke.
That's why he's pumping doge....
If he was pumping DOGE, then Tesla could have bought DOGE instead of BTC, right? The only time when Elon said something good about DOGE was a long time back, when he pointed out that it is somehow protected against inflation because the annual supply is limited. Not even in one occasion he mentioned that DOGE (or for that matter any of the altcoins) is a good investment option.
On the other hand, he has continuously tweeted about Bitcoin in an overwhelmingly positive tone. Even in this particular tweet, he is actually saying that Bitcoin is better than fiat cash. My point is very simple. Elon regards DOGE as a joke and Bitcoin as an investment option. Those who believe that Elon promotes DOGE will regret about it later, when DOGE ends up similar to XRP.
You are right in what you say, Elon Musk promotes Bitcoin because he is clear that it is a much better investment option than even relying on fiat money, in fact without going too far, some Gold lovers consider that Bitcoin is an investment almost safe haven, of course many discussions have been generated around this issue, but certainly Bitcoin is taking a ground that it should have taken a long time ago, even when they talk about Doge the fact that Elon took it into account was a plus for his pump, but we must know that Doge has always been a pump and dump, it is normal, but we must highlight the influence that someone as famous as Elon Musk can unleash worldwide.
FIAT money is known to generate a lot of debt, it is impressive what has been unleashed, some economists say that a fall in the world economy will soon come or is looming and this has generated diversifying the money for both gold, real estate and bitcoin.