A short, straight, $1000 a month type proposal is the ideal way to mainstream a UBI as an idea. Nice round number, simple framing, actually is non-budget busting as it's a concrete figure, etc. It is a conservative proposal, it's similar to things Nixon and Reagan both toyed with (among others) as welfare alternatives, but that's why it has political value. Kinda like the universal mandate once did.
The "Fair Tax" had millions spent on it in both design and marketing and nobody still knows how to calculate what the prebate would have looked like, let alone when it would apply. And this was, again, treated as a serious policy plan with tons of various models run trying to make the things work not as a GOOD policy but in a way that actually could happen.
A "living wage" means nothing. A job "guarantee" demands infrastructure. Raising the minimum wage is a widely admitted ineffective policy versus all kinds of alternative anti-poverty or income policies for anyone who doesn't have it written into their contract.
Imagine if the Alaska Permanent Fund was predictable quantity. (Imagine if sovereign funds couldn't be raided on a whim by legislatures.) Imagine if the base cash part of Bolsa Familia applied to every child. Universal programs don't gain universal acceptance until they're actually perceived as universal and at least predictable if not permanent. This is why Medicare For All keeps its appeal and is becoming a form of litmus test in the Party despite being no less ideal by any respect than Yang's prospective.