Because it absolves them of all responsibility.
For example- go ahead and smoke six packs a day. If you get lung cancer, it was just "god's will."

All this god's plan stuff, some f---ing plan!

There is such a desire for there to be cause and effect in our lives - and sometimes bad stuff happens for no good reason.

Frankly I think when I realized that - that's when I firmly became an Atheist.

As for God's plan...

I think of how God had not planned for Adam being lonely and needing a woman. So in all his omniscient wisdom, God parades all the animals before him so he could choose a mate (can my eyes roll any further into the back of my head?). After figuring out Adam needs a woman, he then creates Lilith. God failed to realize that by creating Lilith from the same material that he created Adam from, Lilith was every bit Adam's equal...and that just could not be left alone (God apparently is not all powerful because he could not simply change Lilith, and he was restricted by his source material. Plus, he should have known this too!). So God banished poor Lilith and created Eve, who , unlike Lilith, does not seem to have a brain

Saw another cartoon like this, rather more elaborate, along the lines:

1. Make universe
2. Establish periodic table and physical laws
3. Create humans, endow with self-awareness

... and a bunch of other steps. As God considers this list, he muses, "Hm, if I have little Mary's dog run over by a car right HERE, this might all work!"