The reason why I think only A sides would be more entertaining is because A sides is what most players have actually played during casual playthroughs, and anyone that has watched speedruns of this game are more used to seeing the A sides done in the any% routes. So alot of people including myself may not find B sides as entertaining.
There’s also the question of what happens if in the future, it’s discovered that doing all B sides ends up being faster than doing A sides at all, or at least doing a majority of B sides (like 5 b sides). Of course that seems silly now, but I feel that this could set a bad example sometime in the future if this run gets further improved or if a simmilar movie has the same issues.
that's not how the speedrun works. those 2 b-sides are the only b-sides that are even CLOSE to being faster, with the timesave on the chapter 6 b-side being so small in RTA that no top players even go for it in runs.
in addition, there is a separate category which is any% except you beat every b-side instead of every a-side, and the world record is almost 11 minutes slower than the any% WR.