It's not even a matter of 1500 years.
All the Reformers - Luther, Calvin, Melancthon, Knox, Zwingli, Bucer, Chemnitz, etc. believed in Mary's perpetual virginity.
The vogue for denying Mary's virginity really dates from 1854, when Bl. Pope Pius IX proclaimed the immaculate conception.
Since that time it's become increasingly popular among many Reformed Christians to deny Mary's perpetual virginity.
The response probably has more to do with the declaration of papal infallibility during Vatican I. Given that the pope declared the doctrine of Immaculate of Conception ex cathedra, which has nothing to do with the dostrine of the eternal virginity of the Virgin Mary, that's probably what provoked/provokes the attacks. Because the Reform are ignorant of this fact, it's no wonder that they've made this into a strawman.