If you look closely at the official EF scale DIs, the absolute maximum that an average frame home can be assigned is 200mph (high EF4) without using the slider to bump it toward upper bound - which requires 'superior' construction above the building code. The problem with that is not only the rarity of 'superior' homes, but that a 'superior' home has to be hit at PEAK intensity, and be located somewhere that the WFO doesn't assume failure mode was due to other non 'superior' homes nearby disintegrating and pelting it with debris. AND, of course, being in a WFO that will even acknowledge it. Given all that, you can see why EF5s are so rare, especially when frame homes are about the only major DIs to go off of.