From the article:
Is British Airways desperately trying to stop its passengers running up huge bills by visiting the superior Cathay Pacific and Qantas lounges in Terminal 3?!
While it's true that the definition of 'huge' is unscientific and depends on the person, I personally doubt that it is the case.
My bet, personally, is to do with punctuality. T3 has always been bad at punctuality - a mixture of infrastructural constraints, type of routes, transfer flows, some localised self-harm by BA themselves - and what I'm hearing now is that it's being even worse these days. If you have the possibility why not concentrating your flying in T5? BA right now is still moving quite a lot less passengers than it did in 2019 (the last I heard, from early June, was that the overall number of departing passengers ex London - excluding LCY - was still lower than the T5 figures on a peak day pre-Covid) and there can be enough capacity to handle everyone in T5.