Who were the people who voted for these planes and why are they not flying them all the time?
I'd guess the people mostly voting for the B-29 were the last ones who could actually afford flying one

300 perks for a formation are quite a risk for the majority of players, and that's why they have to fly very high. But that takes more time than many are willing to invest. Lacking a really attractive (for the masses) strategic target, the 29 is practically a plane looking for a job.
And the 410... well, folks are slowly realizing that their awesomely armed fighter... isn't really one

(I will present a detailed analysis on 410 usage over time after the end of this tour)
Nobody wants to spend 30 minutes climbing to be wonder-bb pinged off the sky by a buff.
But on the other hand, a plane with a perk price like that (p/o the other guy if you kill him) and a very juicy ENY of 2.0 is quite an attractive target. I have done a number of B-29 strat runs this tour, and my guns saw a lot of use, despite flying at 28-30k