This hidden agenda issue can be very problematic, as you say it might be self-evident based on watching people leave that they've gone somewhere else for the "better" tech stack but you'll unlikely to get anyone to admit to it, unless you're working somewhere progressive and/or with a progressive manager etc.

My last place we intentionally didn't use K8s but we were upfront with our team and hires (it was almost one of the first things I mentioned when recruiting) along with the reasoning.

But unless people are honest about their motives, and this is something that has to cascade down from the top, you'll get all sorts of sabotaging behaviour, especially if OKRs are imposed from the top and not bought into/negotiated across the org.

This gets worse when (due to human psychology and fast brain/slow brain traits, with the slow brain backing up the knee jerk fast brain) goals like the ones you mention are hidden (in shadow - see Jung). Or as mentioned in other comments you get the whole Economics externalisation problem when all sorts of 2nd and 3rd order+ goals (like team/org cohesion, fixing technical debt, taking ownership of incidents/problems or going the extra mile) which aren't in any of the OKRs get gamed out of the system because no-one's tracking them. This would be fine if the OKRs are light touch guides and not excuses to stick everything else on the bonfire. i.e. OKRs are in service and not master.

I'm not sure how you mitigate this other than hiring people aligned with company values/goals/action who are less likely to just be (understandably because it's a jungle out there) maximising their pay and the modernity of the tech stacks they know and foster a culture of co-operation not competition.