There's a story that's told about why modern game controllers have the directional inputs on the left side. Supposedly, arcade games that used both directional inputs and buttons originally placed the directional inputs on the right-hand side, because most people are right-handed, and directional inputs typically require more finesse. But at some point, some arcade owners allegedly started switching this around (which is a very easy thing to do, requiring minimal DIY skills) in order to deliberately force the right-handed majority to play with their non-dominant hand on the directional inputs, so that they would have more difficulty and therefore have to spend more money to progress in a given game. This would probably have been around the 1980s or early 1990s. Eventually the industry standardised around this, and therefore we now have the standard control layout that places the directional controls on the left.
But is there any evidence of this claim about arcade owners modifying their games in this particular way? This story is very persistent, but I have yet to find anyone actually citing a source.
If you don't get an answer here, you can try arcade collectors to at least answer the question, "Does there exist a lot of arcade machines that have been modified in this way?"
Collectors will be very interested in when something still has factory-original parts, so if this sort of modification was widespread, I would count on collectors being aware of it. I've seen collectors note that a cabinet doesn't have the original T-molding or the buttons are the wrong colour, so something like the joystick being in a different position wouldn't avoid notice.
A lot of the controls also came with artwork, indicating what each button did. Look at the Joust controls here, where the button has the "flap" and wings around it:
https://www.arcade-museum.com/images/118/1181242123211.jpg
Or this Space Invaders control panel (note the arrows next to the movement controls):
https://www.arcade-museum.com/images/106/1067262713.jpg
Or this Defender control panel (again, up and down arrows next to the movement controls):
https://www.arcade-museum.com/images/118/118124210297.jpg
It would interest collectors if they had the original artwork, so I think that's another reason they would take note of this modification.
Now, what exactly motivated the industry to standardize around one layout versus another is harder to answer. But whether or not there was a widespread trend of these machines being modified in this way should easily be answered by people looking at the machines themselves.
