I think it's because while you're asexual, your romantic preference is dudes, right?
If you're on a dating site that caters to heterosexuals, and start to chat up girls, you're barking up the wrong tree, because most girls looking to match with guys on Tinder are trying for a hetersexual sexual relationship, and might feel like talking to you is a waste of time.
Like nush said, you'd probably have more success on Gridr, and make sure you put asexual in your bio so that you're not leading anyone on.
Another alternative is Bumble BFF.