Working with many non-profits, they're very careful to keep expenses below a certain percentage of their donations. Otherwise sites likes these cause them to lose donations.
Unfortunately this results in low salaries for employees which means the employees gain skills but can't afford to keep working there. The non-profit loses talent they helped build.
I know of some non-profits who have gotten around this by creating a 2nd non-profit where they receive donations just for business & administrative costs. Than use their 1st non-profit to say 100% of donations goes to our causes.
In reality, you should get to know your non-profits. Volunteer & help them out. Then you'll have a better understanding of how they use their money. Sometimes those high administrative costs result in a lot of value being achieved, even if the percentages don't look great.
Personally I'm a huge fan of a lot of community non-profits like local YMCA's if anyone is looking for a good place to start. I also tend to work with other small, local non-profits.