That whole thing about Kushina/Mito having special chakara powerful enough to suppress Kurama really created some misunderstanding in the fanbase.
Sure, you need a powerful enough body to host a bijuu, but that body doesn't have to be from a clan that specializes in body/vitality. You noted that Madara and Obito had Hashirama's cells when they became jinchuuriki, but the truth is, they could probably be jinchuuriki even if they didn't have Hashirama's cells.
People seem to think that just because Kushina/Mito were chosen because of their bodies, means that all jinchuuriki need a Senju/Uzumaki level body.
However, I think a lot of people forget that a bunch of people who aren't even from any special Otsutsuki related clans have been jinchuuriki and been perfectly fine (with some of them even becoming perfect jinchuuriki). Examples of this include:
Bee
Gaara
Yagura
Fu
Yutakata
Yugito
Roshi
Han
Rin
etc...
Now, whether or not these people could host specifically Kurama, I'm not sure.
However, you don't necessarily need a special body to host a bijuu in general.
Kushina/Mito's special chakara thing simply made them exceptionally good candidates for becoming jinchuuriki (which is why they were chosen), but it isn't a requirement. Think of this analogy:
Someone with the iq and education of Albert Einstein would certainly possess the ability to teach a math class. In fact, they would almost be overqualified!
However, just because Einstein would make for a highly qualified teacher, doesn't mean that someone of a lesser iq (but still the right mathematical skill) wouldn't be qualified for the job.
Now for those who don't understand, in this analogy:
Einstein's iq/education represent Kushina/Mito's special chakara/bodily power.
Teaching the math class represents being a jinchuuriki
The other teacher's lesser (but still qualified) iq represents a body like Bee's or Gaara's, that is still strong enough to host a bijuu despite not having special chakara or being Senju/Uzumaki level
Having said that, going to the question of why hasn't a Senju been a jinchuuriki:
Well, my answer is: Why should they become one? Why should it be specifically a Senju? There are 9 bijuus in the world, vs billions of humans. There are many humans that could easily host one of said 9 bijuus, so there is no reason for Konoha to specifically target the Senju for making them jinchuuriki. Plus, the bijuus at different points in time were scattered around different nations, so places like the land of lightning for example would obviously choose one of their own, rather than a Senju.
