I applied two coats of "top quality" driveway sealer last fall (one
coat using Home Despot brand and 2nd coat using Sears brand). The
buckets said that the sealer would last for 7 years.

Everything looked fine until the snow melted and I noticed that the
sealer is peeling away in several parts of the driveway.

Why is it peeling after just 6 months?

(Note I washed the driveway as per the instructions just before
applying.)