Good OKR should be value-based, not a set of activities or a to-do list. However, on the personal levels, your employees usually don't have a metric that they can fully own and be responsible for. Building a company and a product is a team sport. Your whole engineering team works on the next release; the marketing department works on increasing brand awareness, etc.
If you force such OKRs, your co-workers would most likely set small activity-based tasks that they can do themselves. It would make most of the OKRs look tedious, too detailed and not providing value for anyone from the outside. So your OKRs wouldn't be referred to as a reliable source to understand the team direction.