Its the fireing sequence multiple of 4,V8 ignite two pistons at a time. Engines run in 4 strokes that produce vibration and equal energy lost to produce the them, 5 or 6 cylinder help overcame unuseful strock inertia. That why in F1, V10 became standard it runs more efficient that a V8 or V12.
Tell that to NVdave. He thinks the only motors worth building are straight sixes or v12s.
But now that you mention it, I have seen alot of large industral generators and pumps with v10 motors. And when I industrial I don’t mean a farmer’s irrigation pump(like NVdave talks about). I mean pumping stations for the gas company or electrical generation for small towns.