Why would we be? Microsoft didn't lie to us about this. It is ultimately disappointing that Forza Horizon 5 is likely built with the Xbox One as we will hopefully learn next week if it is shown but this. Conversely, when Gran Turismo 7 was announced it was announced as a PS5 exclusive.
They boasted about generations in tons of news articles, basking in the glow of the good press that was generated but when it's time to show your hand, it was done in a blog Q&A which is the equivalent of the Friday news dump at 7pm. So, not only did they lie, their actions were cowardly on top of it. It makes perfect sense to have GT7 on the PS4. They should have said it from the get go.