Your peers are rewarded for accomplishing their goals. In the best-case scenario, the incentive is to find ways to synergize your goals so you are all benefitting.

In the common-case scenario, you figure out how to bribe / cajole / coerce them into putting time in on your project and don't really care about how things are going on their project, because we're all responsible engineers who can time-manage ourselves, right? So you get your promotion and they get screwed because the work they did to deliver on something valuable to the company isn't reflected in their OKRs.

It degenerates what should be a collective goal of accomplishing the company's objectives the best way possible into a slotting game of making sure you're always listed on paper as being on the right project, because your work won't have value if you applied it outside your bullpen.