Why are hydraulic roller lifters, different on different sides in the engines?

It's easy. Either somebody had a lifter go weak at some point and only replaced the failed units with a different brand/source/production run of lifter...

Or Chrysler had a vendor change and different styles of lifter got mixed in the bin.

There are NO variance in the part numbers in the catalog, and there's no significant difference in oil pressure to either bank, but if lot A comes from Jim Bob lifter company and lot B comes from Chrysler lifter manufacturer facility they're gonna be different. I guarantee that Chrysler does NOT care how they're made, as long as they spec correctly for fit and function.

And that doesn't even include revisionary changes.

This can easily be compounded with an export vehicle where replacement parts could be from a whole different country than anything available here on the US (brisk spark plugs come to mind).