I don't understand the question? I always start with dried peas that are already split.

I feel like the one time I made split pea soup, the recipe I used started with split peas. Like these ones:
http://www.amazon.com/Green-Split-Peas-lb-bag/dp/B002W7OUUA
You start with them split. I'm not sure what the problem the reader is having... I think she must have started with dried peas instead of split peas?

How old are the split peas? If they've been sitting around the shelf a while, dried beans (and split peas) can get dried out, so then they don't cook very well.

Also, you might just have bought them, but they could have been sitting on the shelf at the store a while.

Yeah, split pea soup is made from split peas. The peas are split in the drying process, long before you buy them. cf. Split Peas

I think your question might be asking why your peas didn't turn to mush and disintegrate. I know it seems dumb, but is it possible your crock pot was on warm instead of low?

If you have more split peas from the same bag or batch, try doing some stovetop and seeing if it turns to mush after an hour. That'll tell you whether it's the peas or the crock pot.

If your problem is that the soup didn't get mushy, could it be that you didn't add enough salt? Salt helps dried beans cook faster, by making their cell walls break down faster. If you reduced the salt in the recipe that could be why.

Kitchen can be full of surprises and mysteries. For example the time I prepared couscous, except it was sesame seeds! Both good things but not interchangeable.

I don't think the problem would be not enough salt - salt added too early while cooking beans actually actually makes it harder for the beans to absorb water, making them tougher. I've learned that it's best to add salt about 20 minutes before the soup is done.