Just nature of the beast I think. Not all of our tractors visibly leak, but they all need to be topped up now and then.
There are dozens of potential leak points on the tractor itself, and more yet on your implements. Chances are that at least a couple of them are seeping.
Most slow leaks manifest as a buildup of grime, rather than a drip.
You will also get some drool from the quick couplers, some more than others.