Because they saw what happened with Xbox One this gen. It's easy to fall from grace if you are outpriced and/or outperformed. Chances are Sony can either take a huge loss on PS5 to sell an underpowered console at 399 or they can sell it at cost for the same price as XSX, which could be 30 % more powerful. If they were confident in their package they would act like it. But since April 2019 they have done nothing but shift the messaging away from power and towards everything else. Even when asked directly about performance, Cerny answered "but the real important thing next gen is the SSD". That always seemed like a weird strategy. And then it was the great new functions of the controller. To this day Sony has not said a single word regarding PS5's power. Not when Microsoft back at E3 2018 claimed they would build the fastest next gen console. Not when since E3 2019 Microsoft advertises the fastest console ever made on their website. "Project Scarlett will set a new bar for console power, speed and performance". They didn't even chime in after DF put XSX at 12 TF and said a simple "Us too". They walked away from E3, So they don't have to show their hand at the same time and be announced the loser this time around? Sony knows how it felt at E3 2013. And they sure know how it must've felt for Microsoft. Not exactly the position you want to be in.
Basically the longer Sony is silent, the more realistic the performance gap is. The possibilities so far range from 12+ TF PS5/10 TF XSX all the way to an 8 TF PS5 with no VRS, a GPU Compute based raytracing solution/12+ TF XSX (which would put the XSX at an actual real life performance advantage of 80 % vs PS5). One of them likes to talk a lot about performance (it eat's monsters for breakfast), the other not at all. Sure, Sony could be the one playing games. But then again they had devkits out there 12 months before Microsoft. What does that tell you about how far they are into development? All that insider talk about the two being close to one another is not at all what their respective messaging says. Which is that Microsoft just oozes confidence while Sony is scared as shit. That's the public image they are currently showing. Maybe for a reason.