- Rules that impact whether a product or service can be sold in the EU
- Rules that determine how that product or service would be produced if it were made in the EU
They're not the same thing.
Factories abroad have to align with the former to sell into the EU, but (unless they committed to in a trade deal) not the latter.
In Services for example, the UK could voluntarily align with every EU rule and standard... It still won't have the right to sell insurance to those on the continent unless the EU permits it (which they are not obliged to do).
Even if you adopt all EU rules unilaterally, the EU still gets to determine what (potentially costly) tests and evidence it needs to see before it accepts a consignment as EU safe.
That's conformity assessment.
It can mean unilateral adoption.
It can mean an agreement not to lower standards from where they as tree now.
It can mean an agreement to replicate EU rules in the UK as they're made.
The less you align with the EU by treaty, the more onerous it's likely to be for UK businesses to prove their products do, and the more reluctant the EU may prove to provide goods and services access.