That's my guess. Picture a typical engine crankshaft driving a piston up & down via a connecting rod. Its converting rotational motion into 2 way constrained linear motion. Now if a belt were connected to a slider block (piston component) and looped over 2 sets of pulley wheels and the belt was open to accept the blade holders... I think that satisfies the up & down blade stroke in sawing mode. Larger crank pin radius = longer stroke. This way the motor always goes in one direction, you don't need complicated reversing mechanism. But of course you can vary the rpm for slower/faster stroke. But to keep the belt in tension & blade aligned & easy on-off for piercing the blade into inside pilot holes... thats where the R&D comes in!

I'm always fascinated that 'good' scroll saws like Hegners seem to be able to cut metal & more challenging materials with precision whereas other saws of the same power & dimensions frame rigidity etc. just don't seem to cut as well. Hegners cost a fortune here so I will never know, but makes me wonder if it has to do with blade action?