The aspect that makes it shirk is that the people asking for help from the Jinn either admire or fear the power of the Jinn (admiration and fear being parts of Worship); this is the only reason they turn to the Jinn to begin with. They want "special information" or "special healing" or "special protection" etc... (that they acknowledge fellow humans cannot provide) and rather than asking this from Allah (ﷻ), they ask this from the Jinn based on their view of the Jinn's power. This is Shirk. -- Little do they know, most Jinn are liars and employ magic.
Moreover, many of those who turn to the Jinn may also fall into a second kind of shirk when interacting with the Jinn; the Jinn, in exchange for doing the favor for the human, may command the human to do something in return - something that violates Islam. Following such a command constitutes shirk.
‘I have created all My slaves with the inclination to worship Me alone, but the devils come to them and turn them away from their religion. They forbid to them that which I have permitted to them, and they tell them to associate others with Me for which I have not sent down any authority.’” Narrated by Muslim (2865).
In contrast, when asking a fellow human for a favor... you acknowledge that the human doesn't have any special power or special ability and you do not admire or fear him. Not shirk.
Hope this helps. وعليكم السلام ورحمة الله وبركاته