That's because they gave their tithing with a wrong revelation.
A lot of people give with a sense of unjustified self importance.
The right way to tithing is to give with these sense of revelation;
1. You recognize and acknowledge it is God who gave you the power to gain wealth
2. You recognize and acknowledge if God had not opened that door or made it possible, you would have not gotten that Job or income/business/project.
3. You recognize and acknowledge that all the money and your belongings belongs to God
in the first place.
When I give, I give whole heartedly without compulsion. Even if I don't tithe, I know God does not condemn but I only give opportunity to the devil to devour.
There is not about Law.
The Book of Malachi does not say God curse you with a curse but because you don't tithe, you subject your money to the world that is already cursed from the beginning.
That is what it means in the book of Malachi. Some Christian misinterpreted that meaning in Malachi to equate it with the Law.
However I just want to testify to the Glory of God it is out of his
goodness (of Father God), He has been faithful to bless me back (financially) according to his word in the book of malachi. The windows of Heaven's blessing was opened to me and so far has remain open to my life. I'm not saying this to twist anyone's arm to tithe. I'm saying this to testify that God is not a liar and is faithful to his word. This is something that is real and not just wishful thinking.
But why is that when some of you tithe, you don't see this blessing? Check your revelation. When you have a wrong revelation, I believe the HS will not work according to that.
Does it really necessary to give at least 10% of your clean income for the month for tithe?