Only recently have panel gaps become a big deal to typical owners.
In the 70's American and European vehicles had much larger panel gaps. Doors clanged shut, hinges creaked, and there was a significant variation in measured panel gaps around the car. Shocks were terrible, springs would sag over time, paint would often have sags, Exhaust systems lasted only a year or so, bias belt tires flat spotted and lasted only about 12,000 miles. Big cars wobbled down the road and handling was only available by increasing ride harshness. AM radios had knobs of push buttons and a big upgrade would be a rear speaker with adjustable reverb. Individual vent windows tended to whistle at speed and hand crank windows were standard. Had to reach across to each door to press down or lift up a locking button. Annual tune ups with carburetor adjustments, plugs & points replacements, tire rotations and new brakes was not unusual.
Europeans followed Mercedes lead by engineering a solid THUNK into door closings. Made consumers feel like the cars in total were better made. Seat belts were only lap belts, no air bags and often the dash was metal, and covered by paint. Bodies tended to begin rusting immediately, and where salt was used on the roads they could develope rust in only a few years. Owners would have aftermarket Ziebart spray tar based rust proofing to slow down the corrosions and make their loosly assembled cars quieter.
The Japaneese were perhaps the first to market wil better panel gaps. Their motors and bodies were put together like jewelry. Panel gaps began to become a marketing issue and people began to take note of what could be possible. These cars tended to be smaller and had less acreage to make alignments better.
Paint was getting better as well. Instead of a single coat of enamel over primer, water based multi coats were developed. They often used metal flakes to add drama and cover everything with a top coat of clear for a deeper look.
Repainting your car was common. Either go down to Earl Schieb (Any Car, Any Color...$29.95) or a trip into Mexico would get you a fresh and cheap respray.
Now, customers arrive at delivery with micrometers to measure each panel gap. They are looking at measurable, not only visible, differentiations all over the car. Want gaps perfectly equal from side to side as well. For some reason this has become the measure of quality in their minds. The car might work perfectly, but they still need to check the gaps.
For manufacturers, making every panel gap the same is hard, expensive, takes lots of time, causes more waste, and really slows down the production line. Companies like Rolls Royce and Bently almost price themselves out of the market by assembling many cars several times to get everything right. A common quote by Bob Lutz is that "too much quality can kill you" reminds people that if the production is not profitable the business will fail.
In mass production price and quality are opposing values. Consumers want their quality to be the best and their pricing the lowest.
Outside of fragile Ego's, having the right and left door jams slightly different do not really effect operations of the vehicle for transportation. Car fittments are often more a matter of pride than utility.
Many vehicle owners are perfectly happy to live with imperfections if it means they can still get to and from work, take vacations and run their errands.
Understand people wanting a well built car, but for some reason reading so many people not only rejecting their cars, but that they somehow take joy in coming to forums like these to kinda brag how they rejected a car because of a panel gap is somehow strange to me.