I'm not an expert by any stretch, but through no fault of my own, I know my way around agriculture, and I know my way around planting and removing trees. Making a forest, a proper forest, is probably the furthest thing from "stamping a bunch of seeds into the ground" you can imagine. You can't even grow trees from seeds manually, that just doesn't work on any scale. You plant saplings that you spend years caring for, and then they die on you and you start it all over. The way you described is the way to get a wild meadow, but the one dominated by some weed monocrop, and exclusively the one you don't want. You will have a country-wide infestation of poisonous hogweed that kills all life around it before you'll get one tree the way you want it to be.
Forest requires very specific amount of biodiversity, soil characteristics, layers of biomass influencing each other, specific insects and animals, it needs tens, and in specific cases, hundreds of kilometers of space, it needs seasonal changes, in some cases cycles of burning, and most importantly, it needs time. Generations of trees need to grow and die and grow and die again in order for a forest to be sustainable and not fragile. Forest isn't a bunch of trees haphazardly put in an empty parking lot, it's a life long project that is not guaranteed to succeed by any stretch.
Europe has the deforestation problem because forests are biomes with their own complicated rules, not a bunch of seeds thrown in an area half a kilometer wide between a road and a waste treatment facility.