robusta has more caffeine and is more tolerant of climates and diseases (robust), arabica has a better taste (original coffee arabs popularized as an alternative to wine).
I would be sad if Arabica wouldn't exist anymore. But seems to be only a matter of time. Nevertheless, I too have high hopes regarding Robusta. I heard, there is a big potential.
There's also a very uncool colonial system involved where many small growers are not allowed to sell or export thier coffee crop without jumping through exploitative regulatory hoops that increase the cost at every step. Not to discount the climate impact on the crops. The added cost comes down to greed in both cases - the ones taking advantage of farmers developing countries and marking up the product more and more and the greed of people profitmaxxing regardless of causing and making the climate crisis worse.