I don't know if the timed exclusive rumors are real or not. But one big thing with timed exclusivity is that you need to compensate the studio for expected lost sales on the competing platform.
With Xbox "not caring if you buy a Series X or not", this is basically open declaration that Series X sales could be so low, Sony could ask for launch exclusivity, while paying far LESS for the privilege.
Or in other words, by Xbox abandoning the idea of console sales mattering, they also lowered the price Sony needed to pay to get timed exclusivity. While at the same time, massively increase the costs for Xbox to retaliate.
Sony just might have bought timed exclusivity of titles that were once too expensive this gen, but was made affordable due to Xbox's decision to go all in Gamepass.
Every action has consequences. Xbox might not realize what their decision are leading them.