The idea of Apple and/or Google just stop selling phones in the EU seems ... unlikely. A quick search tells me something between a fourth and a third of Apple revenue is in the EU, you really think they'd just stop selling in the EU?
Gotta also remember, that even if the EU would allow this, your average phone user would not use it. Just like your average phone user doesn't root their android smartphone or installs Lineage/Graphene/eOS/whatever. Even if it were made easier (or possible) for more phones, the vast majority would not use it and Apple and Google would still make a lot of money.
But in the proposed scenario, there wouldn’t be any technical hurdles or effort required by the phone’s owner - you could have this be a service offered by businesses. Maybe even the place that sells the phone would pre-jailbreak it for you.
Gotta also remember, that even if the EU would allow this, your average phone user would not use it. Just like your average phone user doesn't root their android smartphone or installs Lineage/Graphene/eOS/whatever. Even if it were made easier (or possible) for more phones, the vast majority would not use it and Apple and Google would still make a lot of money.