Surely, you could overwater them, seeds could be planted too deep, inferior seeds, fluctuation of temperatures (too hot during the day and cooler nights) or combination of all of those. Seeds need to have nice, warm environment with even amount of moisture to germinate.
I've never had any good luck with seeding directly into the garden. After numerous trials, I'll be happy to share what works for me (every time)... I believe (and after many trials of various ways of germinating the herbs), indoor germination provides stable, controlled environment, giving the seeds and young seedlings exactly what they need.
Right now, growing the second round of Mammoth Dill (for pickling of cukes mostly)
---I start with 3oz plastic cups (for mouth wash I guess?)
---Make 3 small holes on the bottom edge (base) - for drainage and watering
---Fill the cups 2/3 with the soil (soil should be fine, well draining and moist)
---Drop 5-6 seeds in each cup (you can thin them out later)
---Sprinkle same soil over top of the seed, 1/4" or so (not more)
---Using spray bottle, I wet the top layer (not drenched, just wet enough)
---I then place the cups upright in the plastic container (any from the Dollar store would do, as long as it's height is 2"-3" taller than the cups. This provides some room for germinated seeds, so they don't bump into the cover
---Cover - either plastic wrap, or if your $1.00 "topper ware" container came with lid - fine too
---On the top of the fridge these go till germination occurs (4-15 days, depending on the variety)
---Once all (well, most) germinated - wrap/lid removed, and I harden them off as any other seedlings.
---I do water them from the bottom, just poor the needed amount of water to the bottom of container, and watch them soak up the water through those bottom holes in the 3oz cups... Otherwise, you take a chance to damage ever so gentle stems at this point
---When I see a first set of real leafs, I use half the recommended strength fish based fertilizer (Alaska 5-1-1 always worked fine for me)
Once the roots are strong enough (usually when herbs are 2"-3" tall and have few sets of real leafs, I transplant them to their final destination.
I hope this helps, try it, you may find it will work for you too.