You don't think there is any benefit in being at the table when regulations are put together, to protect your interests.
If that's your opinion, great. You stick to it.
Imagine the scene - 27 EU manufacturer reps sitting round a table discussing whether their new electrical gizzmo should have a 2 or 3 pin plug. The negotiations will probably take months/years to placate all 27 states. The paperwork will be in 27 languages at enormous cost. In the mean time, UK manufacturers will be doing deals with the rest of the world.