I don't know where you got the information that the RTP has been changed, because casinos usually don't share such detailed information. You can only know the maximum RTP range given by the software provider.
However, my guess is that by watching the casino spend a lot of money on marketing, you can just guess that the money comes from the raised house edge.
Unfortunately, marketing is an indispensable weapon of every casino in the fight for customers. If a casino wants to develop, it has to look for new and unfortunately expensive methods of promotion. We can accept it or just look for another casino.
I think on some games, it is possible to see their rtp. The OP noticed that there is a change or a casino will also give a notice about a change in their rtp. We should not judge the casino early because what if the casino is just successful over the past years of its operations? And they have now lots of money to spend on their promotions. If we cant win after seeing the promotions, then it doesn't automatically means that the rtp have been adjusted but we are simply unlucky.
I like a casino that does regular promotion because it gives me confidence, that they are safe and they will not fail to pay me in case I won a really huge amount.