Hi, there are so many variables when it comes to seed saving and propagation. I'll list some of the more common things that can go wrong, but this isn't intended to be a lecture, or a "you have to do what i say" thing
I work in a nursery and do this kind of troubleshooting for a living, I can't help myself from "helping".
I'm assuming your seeds weren't eaten by a pest of some sort, when birds or rats get into seed beds it's really obvious, all the seeds are dug up, some are left scattered around, half eaten and they really make mess. Peas are too big for
ants to carry away.
I'm not sure what the weather's been like where you are, but peas, especially snow peas, really don't do well in heat and humidity, usually if this is the case, they will just rot in the ground, and if you dig down you'll find a mushy pea or two, or just the husks will be left. They are also frost tender. They like between 13C and 18C, which is about 55F to 65F. They also like a slightly alkaline soil, so I would suggest doing a PH test. It's a really good idea to prepare the soil with
compost, rock minerals, (and lime if you think it's necessary) before you put them in, and make sure that they aren't planted where pea family plants were grown last season. Rotation is usually "leggy, (legumes), leafy, (annual herbs, greens etc,) fruity, (solanums, cucurbits etc), rooty, (
root vegetables)", but I think as long as you just put some distance between this year's and last year's space, you are fine. You can also try planting the seeds in a few different spots. At home, I don't prepare a special bed, I just pop handfuls of peas and beans here and there, next to a
fence, or obliging tree and let them go. The season is so short here in the subtropics, we usually just end up eating the vine tips and if we are lucky we get a dozen pods per vine
Usually, seed saving is the way to go, after a few generations you have a variety that is genetically programmed to do well in your soil and climate. There might be a problem though if the seed you first used was an F1 hybrid variety. Seed saved from F1 seeds isn't
bad as such, but the seed saved from it will have unreliable germination and may not reproduce 'true to type'. You will get a more reliable result if the seed is locally saved, open pollinated (OP) and/or heirloom. The seed companies usually have this information plastered all over the front because it's a strong selling feature, if it's F1 hybrid, they will put it on the back, in the fine print, or not at all. The absolute, best, top secret advice I can give you, is to see if you can find a nice old lady, who has been growing peas in her
yard for decades, from seeds her grandmother gave to her mother, (make sure to offer to chop
wood and listen to some stories in exchange for your magic beans.)
Another thing that may have happened is the seed got cooked somehow, (left in the car, stored in an uninsulated attic etc), or got a fungus or mildew from getting damp. You can store seeds, after they are really dry, but don't dry them in a dehydrator or in the sun. After they are dry, put them in glass jars, with a handful of rice and
Diatomaceous Earth, then store that jar in a cool, dark spot. I have an
esky I store my seeds in. And don't forget to date and label your seeds!! To me, all peas look the same, all brassicas look the same, chillies and capsicums look the same, you get the idea.
Anyway, I hope you have better success next time.