When heroin hit the streets back in the 1980's and burglary/theft became a thing, cars in the UK, built for the UK market with the fuel filler cap on the left would be the ones targeted by thieves. So the filler cap might have been in a great position for when stranded on the motorway due to lack of fuel but it was also in a position convenient for thieves. The first scenario can be avoided by looking at the fuel gauge, the second scenario couldn't really be avoided if junkies roamed the streets every night. You could park the other way round to make the fuel filler cap be road side, but that might not be practical.

I remember when my boss's 'Transit' van was raided for fuel during these high crime times, all the thieves had to do was pull a tube from under the bonnet. I don't think they even had to siphon anything and the filler cap made no difference.

Before this crime wave the idea of locking a petrol tank seemed a bit excessive, who would want to steal petrol, particularly if they had to siphon it and could get caught for stealing? Much more convenient (and affordable) to buy one's own. But then this crime wave of heroin addicts happened so common sense no longer mattered, things had to be zombie-proofed and the idea of an unlocked fuel filler cap now started to seem crazy. Who would invite the world to steal their petrol?

This crime wave also came at a time when people started being truly mobile for work, driving everywhere. No longer did you have the community of normal people walking the streets to make it difficult for thieves, we started to hide inside behind burglar alarms and CCTV. I preferred the former security model where everyone knew everyone else's movements and gossip with strangers duly noted, but such is progress. Note lead was in fuel back then too.

So in the UK it was the natively built Ford and Vauxhall models that were ripe for being raided and the hidden location of the fuel tank made matters worse. Fancier targets, e.g. BMW, would not get attacked even though they contained fuel too, it was the lock on the cap security plus the location that made the difference.