Pivoting when it comes to profit-seeking is substantially different than pivoting when it comes to solving a grievance. For example, when I complain to my bank about a fee or a bad customer service experience, after it's solved, I don't come back and say "Well actually...". On the other hand, if I sell something to someone, I might come back and say "Here's a new thing...".
Unless there are more relevant things to complain about to your bank. Just because they resolved you fee doesn't mean you aren't going to complain also about an unnecessary hold on a cheque or an overdraught caused by an overdraught penalty.
IIUC, the article discusses two phenomena related to charities outliving their original purpose:
(1) (as you mentioned) pivoting to a new cause.
(2) increasing the urgency / direness of their messaging, because making progress on an issue causes their audience to de-prioritize it relative to their other concerns.
Category error.