Pine tends to grow like it's on steroids in hot climates, so the growth rings are very far apart & filled with very spongy, airy material. It really needs time to slowly grow in a cool/cold climate over a good 50+ years in order that create decent quality material for flooring. Alas, it doesn't get that long here anymore, with most trees being harvested after no more than 10-20 years. It's still a good building material for lots of structural stuff, but trees that young are not only a little spongy they aren't very big & once processed into straight stock you don't get very wide boards suitable for flooring. The old tenement boards can be from trees over 100 years old & they're so dense you'd mistake them for hardwood.