IIRC the one of the first times a group put timelines to a fusion reactor they had time vs funding level of something like 20 years/50 years/never, and the funding level that actually materialised was below the 'never' amount and yet it started the 'always 20 years away' joke. Now I think the timeline was probably still optimistic but fusion is also obviously a very expensive thing to develop and while it's gotten a lot of funding it's still at the 'in the background' level.

the PBS Space Time episode suggests to me the housing walls might be the biggest problem

it consumes itself or makes molecules that are destructive to the walls or insanely toxic so can never risk leaks

whatever solution they come up with I suspect it will require a lot of constant maintenance on the first generation