Economies of scale. Post-Brexit, we've copy-and-pasted nearly all EU regulations, because it turns out that a) writing and maintaining regulations is really difficult and expensive and b) there are massive advantages to having the same regulations as your most important trade partners. A lot of people didn't like the idea of EU regulations, but very few people have identified anything in those regulations that they actually want to change.
As a conservative, the whole Brexit project strikes me as antithetical to conservative principles - we abandoned the status quo with no clear idea of what we'd replace it with, nor any clear sense of what the advantages might be. The fallout of Brexit is an incredibly strong vindication of Chesterton's Fence. Shortcomings in EU institutions are a valid justification for leaving only if you're confident that you can replace them with something better; it was only after the referendum that we started seriously discussing what the decision to leave actually meant.
They still apply to us. The only thing the EU rules added were exceptions for undersize bananas which otherwise would not have been allowed.