It does seem that many people think that different rules apply to the charity sector when it comes to spending money on overheads.
An article in Behavioural Scientist https://behavioralscientist.org/the-psychology-of-overhead-aversion-and-what-it-means-for-charitable-work/ is well worth reading; it explains the problem well, and offers an intriguing case study that you can use to get better returns from your fundraising appeals, and especially when you are asking for overhead costs in whole or in part.