As someone who's also in both places, no, they're not really comparable. GameJolt attracts a different audience. I've had more games be successful here and not there than the other way around; your mileage may vary. Why, it's harder to say, but my vague impression so far is that GJ is largely frequented by players closer to the old stereotype of "horny male teenager", while Itch has a much more diverse population, both age- and gender-wise. Have a little patience, and experiment.