The big charities have to be run well and the paid staff at the top do a job like anyone else working for a big company. If they were paid £80k or so to run it then they would probably quickly move on to a better paid role and the charity then has to keep recruiting trying to find someone committed to the cause and willing to work for less than market rate.
I’m not connected to any charity so this is just my opinion. I’m happy to donate monthly to Alzheimer’s Research and they communicate regularly, it feels worthwhile.