Israel did not have to turn away from God but it was prophesied that they would indeed provoke God to anger.  On careful study one can see both the scattering of Samaria in verse 27 and the exile of Judah in Babylon in verses 28-31.  Sadly, just as Moses said it would happen in verse 25, Israel did evil in the sight of the LORD.  After Solomon died circa 975 B.C. Israel was split into two.  Jeroboam became the king of the 10 tribes of northern Israel called Samaria.  Rehoboam, Solomon's son remained as king over the southern tribes of Judah and Benjamin. In 723 B.C. the prophecy of Deuteronomy 4 began to be fulfilled, Assyria laid siege upon Samaria and the ten tribes were soon carried away by Sargon into Assyria never to return.  Today these ten tribes are called "the lost tribes of Israel"

46 Years after Samaria was scattered Judah's cup of iniquity had become full and in 677 B.C. king Manasseh was taken captive into Babylon.  Here is the difference though, Manasseh repented just like it states it verses 30 and 31.  2 Chronicles 33 tells the whole story of his wicked reign, his carriage into Babylon and his restoration after his repentance.  This repentance however was not one that was complete according to the Laws of Moses, he did not destroy the idols he set up, he did not bring his nation to repent and return to worshipping the one true God, and he still was considered a king that did evil in the sight of the LORD.  Therefore the curse of the 2520 was still active in spite of the short reprieve God in his mercy granted king Manasseh. "Wherefore the LORD brought upon them the captains of the host of the king of Assyria, which took Manasseh among the thorns, and bound him with fetters, and carried him to Babylon. And when he was in affliction, he besought the LORD his God, and humbled himself greatly before the God of his fathers, And prayed unto him: and he was intreated of him, and heard his supplication, and brought him again to Jerusalem into his kingdom. Then Manasseh knew that the LORD he was God." 2 Chronicles 33:11-13

Another 2520 warning to the Israelites is found in Deuteronomy 8:

Deuteronomy 8:17 And thou say in thine heart, My power and the might of mine hand hath gotten me this wealth.
18 But thou shalt remember the LORD thy God: for it is he that giveth thee power to get wealth, that he may establish his covenant which he sware unto thy fathers, as it is this day.
19 And it shall be, if thou do at all forget the LORD thy God, and walk after other gods, and serve them, and worship them, I testify against you this day that ye shall surely perish.
20 As the nations which the LORD destroyeth before your face, so shall ye perish; because ye would not be obedient unto the voice of the LORD your God.

The prophecy of Israel's disobedience found in Deuteronomy 31:

Deuteronomy 31:16 And the LORD said unto Moses, Behold, thou shalt sleep with thy fathers; and this people will rise up, and go a whoring after the gods of the strangers of the land, whither they go to be among them, and will forsake me, and break my covenant which I have made with them.
17 Then my anger shall be kindled against them in that day, and I will forsake them, and I will hide my face from them, and they shall be devoured, and many evils and troubles shall befall them; so that they will say in that day, Are not these evils come upon us, because our God is not among us?
18 And I will surely hide my face in that day for all the evils which they shall have wrought, in that they are turned unto other gods.

The LORD can not bless sin, the Israelite nation was brought into their land of promise through a blessing and they were told over and over that He delivered them from bondage.

"And God spake all these words, saying, I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage.  Thou shalt have no other gods before me.  Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth:  Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me; And shewing mercy unto thousands of them that love me, and keep my commandments." Exodus 20:1-6

Today we are freed from the bondage of sin through Faith in God's mighty Grace.  But He can not bless us while we are wilfully disobedient to His laws.  Through Him we are dead to the law; He takes our sin away, He pays the price for our sins and He gives us His victory.  But just like the Israelites, if we choose the sins of this world over Him we are no longer under His Grace and His blessing is removed.  He suffered long with Israel and He will suffer long with you but there are limits.  Those limits are what the 2520 is all about.

"Behold, I set before you this day a blessing and a curse; A blessing, if ye obey the commandments of the LORD your God, which I command you this day:  And a curse, if ye will not obey the commandments of the LORD your God, but turn aside out of the way which I command you this day, to go after other gods, which ye have not known." Deuteronomy 11:26-28