It's history, Yeshua1.I know of no Calvinist theologian that I have read in Systematic Theology that agrees with you here!
James Arminius was a Calvinistic professor who studied under Beza.
He expressed what would become Arminianism and a debate followed. His case was heard and a conclusion made on May 30, 1608. The Chief Justice of the Supreme Court concluded that Arminius' position mostly relating to the subtle details of doctrine of predestination, were of minor importance and could co-exist... [and] enjoined both gentlemen to tolerate one another lovingly".
So in 1608 his view was within orthodox Calvinism. But the issue continued to divide Calvinism. James Arminius died in 1609. His views, at the time of his death, remained within orthodox Calvinism. But in 1610 his followers (Remonstrants) issued the Five Articles. Those following his teachings remained within the Dutch Reformed Church until the controversy was settled in May 1619. On July 5 1619 the Arminian ministers were ordered not to preach Arminianism.
So from 1581 to 1619 the teachings of James Arminius was considered to be within orthodox Calvinism. From 1610 to 1619 the Articles (a more developed Arminianism) was debated but was a part of Calvinism. From 1619 forward it was not.
You need to read better Calvinist theologians, ones who have also studied history. I recommend Wayne Grudem. His systematic theology is very approachable and he knows history as well. You could also consider the late R.C. Sproul and J.I. Packer (although Packer was an Anglican,priest and theologian and if I recall from your comments about Wright you are not fond of Anglican priests). You could also reference John MacArthur (who is a Calvinist, although not a theologian per se) and John Piper (my favorite Calvinist).
In fact, I do not know of a Calvinist theologian who is unaware of this history. Most theologians have had to at least study Christian history (to include the Dutch Reformed) in seminary if not during their undergraduate education.