For much of Jazz, the harmonic changes provide a key forward push. Melodic choices have to work within that framework. In Indian music, there are no harmonic changes to exploit for forward motion or melodic development.
With some "smooth jazz" and some modal jazz, the tunes stay in a single key or mode, and there is more similarity to Indian music, but even there the logic it different in that with Western music, the melodic theme or the rhythm section has a big role in driving things, as well as references to our typical song structures.
With a Raga, there is no theme, per se. A Raga is more like a set of rules as to how you progress though the mode than a melody in its own right. Certain notes are designated for emphasis or avoidance, and for being approached or left in a particular manner. With Jazz, an improvisor is left more free to determine how to proceed.
There is a fine "less is more" quality to a Raga. The constraints and consistency serve to give each note in the set its own personal character or meaning, where in Jazz, even with modal, we are often hearing/thinking about notes as chord tones vs. color tones vs. dissonances, using our familiar key and chord structures as references.
There is undoubtedly a lot of cultural context that I am ignorant about, as well, that add to the differences. Also, the way rhythmic structure is conceived has many differences but I only have a rudimentary knowledge of this. Probably should leave it to someone else to explain.
I'm just responding from the few classes I've taken in Indian music and from what I could make out for myself about what people are doing when they improvise in it.
That said, there are some patterns that turn up in both forms, as well. It's not totally different.