eBay is intrinsically designed to encourage buyers and sellers to leave feedback about individual transactions to allow for a built in peer review system. This system has built into it a ‘trust’ or ‘do not trust mechanism for both buyers and sellers.
Buyers can easily see sellers who ship quality items as described on a timely basis and on the other side of the coin they can also see those who are unreliable. All of this is information is available at a glance because of the simple feedback star rating system. Sellers too can see in advance buyers with a track record of non-payment or malicious feedback and so forth and they can set parameters for sellers to protect themselves.
It is satisfying to see your account tick up positive feedback however on occasion one can feel disappointed when transactors fail to leave feedback. This is nothing to be worried about, in fact it could be very much working in your favour.
eBay requests feedback quite aggressively, therefore if a buyer or seller has opted not to leave any for you, chances are they are not happy. They might not be unhappy enough to leave negative or neutral feedback but may have instead opted to simply not leave any at all. In these cases, no feedback is a case of these transactors having done you a favour so don’t fret, keep buying, keep selling and let your feedback tick up without putting too much energy into thinking about the ones that got away.