The obvious common-sense explanation is that they don't have anything particularly interesting on Trump.
Imagine that you actually had something about Trump that was worse than what he always says in public. (I know, it's hard. But try. Maybe "grab the dick" or something.) So you send the information to Wikileaks, and they just sit on it. Weeks go by, you email Julian, "Hey, what about my leak?" and he doesn't reply.
What would you do?
I think you would leak through another channel. Wikileaks isn't the only game in town when it comes to media, you know. If you're too lazy to upload the torrent yourself, there just might be a few thousand other media organizations that would be willing to take the information.
Since this hasn't happened, I think the least extraordinary and most believable explanation, is that there hasn't been a Trump leak. Are you saying that you have come up with an even more likely explanation, where there has been a Trump leak and a conspiracy between every media outlet in the world, led by Wikileaks, to suppress the information in it?
It's interference when it is being done to influence an election
Ok, fine. But if that's your definition, then even a paid advertisement or giving a speech would be examples of interference. Why is interference considered noteworthy or undesirable? Shouldn't everyone be interfering with the election? Australia has mandatory vote; I think America should have mandatory interference!
Unless that's not what you meant. Maybe you meant that interference implies something unsavory? Oh, but then you don't get to apply it to what Wikileaks did. That's quite a dilemma. Have you considered maybe just stop hating Wikileaks, and being grateful that they've already outed and embarrassed the next president? With Trump destroying the Republicans and Clinton already a lame duck, maybe America can have a real election in 2020. Show me one politically-idealistic person, on either the right or left, who doesn't want that to happen.