Tiny house is not a movement about affordability. It's an aesthetic movement. One mostly participated in by people of higher income.
I don't think tiny house is black-and-white 0% about affordability and 100% about aesthetics. To me it's basically a way for people who perceive themselves as middle class to live cheaply in housing that is a step above trailers, and it's caused by the very high rents in certain urban areas like Toronto, Seattle, and the bay area. You probably don't see a lot of millenials living in tiny houses in Des Moines, Iowa or Cincinnati, Ohio.
Also, not sure how familiar you are with the bay area housing issue, but a lot of it is due to lack of supply + zoning. The state of california recently passed legislation allowing some zoning requirements to be circumvented allowing people to build ADUs - accessory dwelling units - in their backyards, which constitute the vast majority of tiny houses in the bay area (again partly due to zoning... there are very few places in commuting distance of the jobs centers where you would be allowed to build just a tiny house, or a collection of tiny houses, on a plot of land).
Around here tiny houses are priced similarly to similar-sized studios, with some benefits and drawbacks of living in an ADU compared to a studio (detached, usually in quieter residentail areas, less amenities than an apartment building might have, often cheaper). Affordability is a huge part of why people live in ADUs over here
I think the same holds true for most of the US outside of major urban areas. When 1/2 acre costs $30,000 any house you build will cost more than the land.
But I don't think a tiny shack, uh, house, should be called a "good option". It's an adequate option under limited circumstances. The problem is calling it a good option makes "we spent five years fighting for the right to our tiny shack" sound like a reasonable thing rather than one more absurd winkle in the development of this country's housing situation.
When I was a kid my parents had a Westfali and we'd take extended road trips. That was also great.
If you don't like it, just don't do it.