DIY works on the theory that even though the individual[0] acts don't scale, their popularity means a finite[1] number could still (compactly?) cover the population.

[0] the Camiroi in Lafferty's Primary Education of the... (1966) could presumably do everything alone, "do it yourself", but we're probably better to aim at small groups, ie "do it yourselves".

[1] centralisation vs decentralisation is a question of small N vs. large N, and actually small N isn't so bad on it's own, it's just that when N goes down to 1 or 2 it's just as likely to go all the way down to 0.