It's kind of a guess like most things in fighting games, but there's a lot context to the guess, some of which has to do with what your opponent has been doing so far, and some which has to do with spacing in my opinion.
Like your goal in a lot of the time when jumping from range, unless you're playing someone who just doesn't anti-air is to go over a poke, which can be a fireball or some other move with a lot of recovery like a heavy kick. A lot of the time a poke can be predictable because it has a particular advantageous range where they want to use it and you can see them looking for that range before they do. Of course the player can always find that range and then do nothing, but there's only so much time you can spend doing nothing if you actually want to do damage, and here's where you have to look for patterns and rhythms, while also trying to avoid falling into patterns yourself. So for example a lot of new players will always throw a fireball when the spacing is reset after a scramble and you can take advantage of that.
The spacing issue also applies to jumps themselves, they can be more advantageous for example at far ranges where an empty jump will make their anti air whiff, and also at cross up range where anti air can be more difficult. Your opponent will want to move about to avoid these ranges but this is where you use your own pokes to limit their movement. I also think it's a lot easier anti-air when the jumps are predictable and when your opponent uses more of their mid range options to take up mental space it gets a lot harder. Nash for example has so many things he can throw at you in the mid range it's easy to get overwhelmed and eat random dash grabs, and the dash grabs mean you feel pressured to poke and the poke can mean you eat a jump in.
It's also why I think you will land more jump ins with your opponent in the corner, since they can't make space behind them the pressure to throw a bad poke just mounts up.
