It's all about hormones in the plant, the roots will start to blow up again once the plant goes back into veg in 4-10 weeks. Depends on genetics and the care they receive. I just revegged a couple different plants and when I took cuttings off the reveg they blasted out gnarly fishbone roots within 10 days of putting the clones in cups. My reveg plants took a few months to fully recover and grow out enough to take clones off them.