Hello,
Percentages or fractions of wealth dont really mean very much here.
Bill and his wife could give away 98% of their fortune and still have one billion dollars left to scrape by on. I am not suggesting they should do so or be pilloried for not. Only that comparisons can be misleading.
I know that we as a family would, in our opinion struggle, to maintain the lifestyle we expect, if we gave away 25% of our income. However many people in the world would not view our "struggle" as such but would wonder why we lived in such luxury on an income far in excess of anything they could ever hope for.

Personally I am glad that Bill and others do make contributions, to help the less fortunate, there are plenty who dont.

Edit - Spelling and grammar