Given similar complains and conditions a few years ago, and that Germany, France etc have since made improvements, but the UK has only added border controls and added barriers to working, it's no surprise that EU drivers left the UK.
But then Spain didn't tell drivers from all over Europe that they are undesirable and unwanted, create a "hostile environment" for them and their families, and then dissolve our trading relationship with our most important partners.
Drivers also don't enjoy gambling with uncertain paperwork, peeing in bottles and crapping next to hedgerows as they wait for endless border queues, so why would they choose those routes when instead they can drive somewhere else where they're not hated, resented and officially unwelcome?