Side drains are not that bad if you can tilt the engine and it effectively drains completely. My logsplitter has a Briggs 5.5hp OHV engine that has TWO drain plugs with side drains, and TWO filler caps. Maybe this is an access issue for various applications. Here is one side. You have probably seen this. Side drains are on my air compressors as well (compressor oil). I think they have bottom drains or at least "at the bottom" even though the drain plug is on the side.
If leaning a motorcycle like the TW200 on the kickstand gets 99% of the oil to drain, it is at least good for that, and a magnetic drain plug will still work pretty well.
My theory on the B&S 6.5 engine on the Craftsman lawn mower is a contractual thing. B&S probably supplied the engines to an assembly plant for a lower price without those drain plugs, leaving Sears with a few more dollars profit on the lawn mower. That would explain it.