There is a bit more to it than that (I think). First it may have been viewed as 100 watts were just not enough. Also this was Fender's first in house D-class power amp design. Perhaps they didn't want to put the stress of a 4 ohm load on it. The Emincence 12" woofer in the Rumble 100 is not as robust as the later Rumble 112 design. So the woofers are different. Just like the now crazy popular Rumble 210 cabinet, the Rumble 112 was introduced a year later at Winter NAMM 2015 and because of ever tightening production capacity at Fender's Indonesian facility, were built for Fender by Eminence in China. Rumble 410 manufacturing was moved to Ensenada, Mexico. At that time Fender Champion 100 2x12 guitar combos were selling hand-over-fist, and the extreme popularity of the Rumble 500 combo took everyone by surprise. It took a year and a half along with two price hikes to get demand in line with production capacity. All this with a factory running full tilt boogie 24/7. Having the two best selling amplifiers on planet Earth at the same time is a good thing. I don't know how the Champion line is fairing right now because I haven't asked, but I do know the Fender Rumble line is the best selling in the world and that the Rumble 500 continues to wear the Best Selling Bass Amp crown four years in a row.