The obvious flaw of Elon's breeder strategy is not so much quality of the looks, but the values these women uphold. It really doesn't matter how many children you have (as long as you have at least one or two), if these children will not have children themselves. You can have a gazillion of children, but if they all will end up living fruitless, wasted lives, it's as if you had zero...
Mothers with suspected NPD/BPD, mother with a celebrity status and/or fame hungry are obviously not a good material for raising children who want to become parents themselves. Not to mention for boys, an absent father spells very conflicted attitude towards becoming a father yourself. Given our cultural zeitgeist of avoiding becoming a parent even without any clear reason at all, the likelihood of prolonging his bloodline drops even further.
It's also very likely that Elon is on the trajectory of crash and burn. I look at him as a slow train wreck. This in addition to all aforementioned factors can add to a hatred and shame in his children, who would not want to prolong the dubious "legacy" as a result.
tl;dr Elon doesn't understand how to build generational clan/aristocracy line.
in our current cultural climate it might be possible only in highly insular communities
