Wella lot of folk lived under the radar takng advantage of the lax governance. For example you are supposed to register for residence if you are in Spain for more than 90 consecutive days. With that comes an obligation to pay tax unless you can show your main centre of interest is the UK. E.g. you have a house and famly there and just rent a holiday place. People were also using the EHIC as a form of permanent health provision.
The problem with registering was you had to prove healthcare entitlement or private health care and a minimum , not specified, level ofcash/income to show you weren going to be aburden. Not registered might not be eligible for reciprical healthcare up to time of vote or date of leaving EU.
A lot of people spent six months here and sixback in the uk getting thebest of both worlds but without adhering to the rules.
This backdrop caused a lot of folk to give up on the dream and go back. Social services, care etc are far better in the UK.
Ironically, Spain has what istermed a golden visa. Have lots of dosh? Not of EU origin? No problem . The Costas are booming with Russian black money being laundered. Great for the economy in the short term but a disaster in the making. Drug gangs bringing the stuff in for Europe from Africa is now a serious out of control problem. I believe Malta has the same problem with golden visas . Maybe Lizzie knows?