Those people get approximately the same amount of lifespan as anyone else (even less, in most cases). If they use up more of their lifespan making mud bricks (by hand!) rather than learning to read, spending time with their families, or maybe even just having fun, that is a waste of their lives, regardless of what monetary value the local economy puts on their time.

> Then (reinforced) concrete is pretty much the opposite of durable, at least with the current “cheap and scalable” technology we use today with steel rebar that corrode and eventually destroy the structure.

Less durable than unbaked mud bricks? I'm... skeptical, to put it very mildly.