Contradicting your first sentence with your second sentence notwithstanding, unless your job title is "chief information officer", you're not BlackBerry's customer anymore. That it took them until 2018-2020 to mothball the PlayBook is impressive given that they washed their hands of it in 2014.
It would be nice if they cleanly divorced devices from the mothership servers (activation, etc.), but that would require developers and money that they don't have anymore to retrofit the system intended to be shackled to BlackBerry servers to work independently. Moreover, just how much of the PlayBook is dependent on phoning home is unknown; for example, in their infinite wisdom, BB10 proximity sensors are server-bound. Activation aside, the more stuff in the OS that is counter-intuitively online, the more work it would need to make some abandonware platform from 2011 work in 2020.
And, if they really wanted to allow their users to use their devices in full, they would have facilitated superuser access ala OnePlus/Google/etc, but treating the OS as anything other than a black box and the user as anyone other than an adversary is not BlackBerry's style.