Once upon a time, people did go to the local airport for its social/amenity/leisure value; now most terminals have become little more than glorified bus-stops,
Different times. I certainly remember the likes of Manchester being used for "social" purposes by my relatives when I was a lad, but that was almost 50 years ago, when the then new terminal opened
, in the days when there was no real landside/airside divide, so unofficially at least we had the run of the terminal and it's facilities and AFAIR car parking was free ( we travelled by bus anyway). In most modern major UK airports the plan is to get passengers only through the security "firewall" and into airside ASAP, hence the location of the shops/social facilities - which of course makes them completely inaccessible to casual visitors/family and friends of pax. As for the cost of car parking...
As I suspect you know some of the larger French regional airports still have some very good restaurants landside that do attract local custom, especially for the long lunch - and they also don't charge a fortune for short term parking or refund the fees for those that dine.......