Kulaks were the stated problem, the real problem were the middling farmers. If you're a smallholder with a surplus of land, your production is very elastic.

You can plant cash crops and sell them to buy industrial products. Or you can plant crops that boost your quality of life directly: fruit, vegetables, tobacco, animal fodder.

The "price scissors" (low price of wheat, high price of goods) meant that middling farmers stopped planting wheat that the USSR needed to feed the cities and to pay for imports. To make the peasants plant wheat again the Soviets took away their land in the name of economy of scale (collectivization), but the real goal was to limit the size of personal plots.