Answer: There are two possibilities I can think of, and both are long shots. One is that instead of a crabapple you have an actual apple tree. This could have happened in two ways, one that you received a mislabeled tree and the other that the crabapple was grafted and at some point the rootstock (an apple) overtook the grafted crabapple top. An apple might not start to bloom for five to eight years.
The second is that for some reason the location is too cold or too exposed for the tree. A few varieties are a bit less hardy than most. In either case, there really wouldn't be too much you could do.
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