I understand that that is the Calvinist position. But does Calvinism give a reason as to why God wants some men not to be saved?
Scripture gives the reason.
"Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth.
Thou wilt say then unto me, Why doth he yet find fault? For who hath resisted his will?
Nay but, O man, who are thou that repliest against God? Shall the thing formed say to him that formed it, Why hast thou made me thus?
Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour?
What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved.
And it shall come to pass, that in the place where it was said unto them, Ye are not my people; there shall they be called the children of the living God.
Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:
For he will finish the work, and cut it short in righteousness: because a short work will the Lord make upon the earth.
And as Esaias said before, Except the Lord of Sabaoth had left us a seed, we had been as Sodoma, and been made like unto Gomorrha.
What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
As it is written, Behold, I lay in Sion a stumblingstone and rock of offence: and whosoever believeth on him shall not be ashamed." -- Romans 9:18-33