all this is from 2015.....
in many markets things have change and some kind of flat rates exist. Or at least offers with a few x000 minutes.
Then, many cheaper phones do come as dual sim but people don't use two of them any way.
The most recent info I found was from 2017
https://deviceatlas.com/blog/dual-si...one-usage-2017
but again, those are just percetnage of existing phones but not how many of them use two SIMs at the same time.

And finally, there is a question of how many people that do use two SIMs (and that is usually just because of the cost) are potential buyers of phones with niche OS with outdated HW and with the price 5x higher than comparable one running android.