It's not unusual for long-running charities to go through a bit of a painful 'adapt or die' stage, particularly if the original founders are still involved.
Charities have to adapt to stay relevant, even if their core purpose remains unchanged. For example if you are running an animal welfare charity, your core purpose can remain largely unchanged but how you attract interest has to move with the times. A good example is RSPCA advertising on terrestrial TV channels which are increasingly not watched by a younger audience - but they need new donors and sponsors, so consequently they will have to re-think their long term advertising strategy.
However in Sentebale's case, it's been running for almost 20 years and during that time not only have their been medical advances in the treatment of HIV/AIDS, but also geopolitical changes which have affected corporate donors. Consequently lots of firms, especially in the US given the current focus on DOGE and 'anti-DEI', will be looking at where, what and how much they sponsor.
The change in focus to include a wider remit for Sentebale makes sense, but the legacy sponsorship through polo matches has been anachronistic for some time now; rich mostly white men, playing an elite and VERY expensive game, to generate charity donations - throw in some animal welfare concerns and from a reputation risk perspective it's a ticking time bomb.
But when your founder and main patron is still involved in the charity, they are more likely than not going to be resistant to someone coming along and telling them it's time to change direction. I've been involved with a charity that had this 'founder syndrome' and it was a lost cause, which was a real shame because the charity was otherwise doing great work but the founder refused to let go.