the others have described things well so read them first!
the irs looks at large charitable donations with suspicion because it is easy for a charity to pretend to do good but really just things the donars would do anyway but now they can deduct it. Thus large donars often have to do a match of smalaer donars as the large donation with no small donars suggests only the rich care and so maybe it isn’t really charitable.
remember the above is a factor in some cases but shoud be considered only after you exhaust the other reasons to do this and find they are not enough.
Rates are not high. 20 years ago they were higher yet - and people are cheering the historically low rates. However if you don’t remember 20 years ago it is easy to think they are high now when in fact they are probably closer to normal.