Do you think Calvin invented TULIP or something?
The truth is, TULIP was formulated not as a positive affirmation of doctrine, but as a negative response to the Arminian controversy. A "new system of belief" was stirring controversy, called Arminianism. A synod was convened (called the Synod of Dordt, google it) to examine those beliefs in light of scripture. The Arminians put forth 5 points of doctrine. The synod, one by one, issued a response (and rejection of) each of those five points.
T to refute the Arminian's first objection.
U to refute the second..
L to refute the third..
etc..
TULIP came about as a negative refutation and response to Arminianism. This synod happened long after John Calvin's death.
So it's not as if John Calvin sat down one day and said "hey! I think I'll invent some new doctrine and call it "TULIP" and "Calvinism!" Such a notion is absurd. It not only demosntrates extreme ignorance of actual history, but is absurd on the face of it. John Calvin a "Reformer", lived amonst the other Reformers, who's job was, you guessed it, to reform the church back to it's original roots. Their job was not to "create new doctrine", but rather, re-establish "old doctrine". If they encountered "new doctrine", they automatically dismissed it as erroneous. So it's not as if anyone "invented" TULIP or Calvinism, because then it would have been "new doctrine", and the Reformers would have rejected it.
The reformers were trying to reform (not revolutionize) doctrine. If you trace church history backwards through time, you can see Christians as early as 529 AD affirming some of the same truths that the Calvinists in the 1600's did, such as predestination and monergistic regeneration. (do yourself a favor and google the Council of Orange 529 AD)
Calvinism is simply a re-estaliblishment of very old Christian doctrine that had been corrupted and lost in the dark ages of the Roman Catholic Church.