They did. Developmental state for huge country = phases measured in generations. 1.4B can't get away with building a few industries like other tigers, JP/SKR/TW/SG who can capture a few highend and do fine per capita.

TLDR timeline

50s-70s was soviet engineers / knowledge transfer from post war wreckage. Built basic industry, 80s-10s was relentlessly building out every industrial chain for every sector except leading edge because lack talent. Talent pipeline was 90s-00s building out academic system, 2010s-20s was brrrting tertiary talent. Couldn't brrrt tertiary talent without teaching peasants literacy in 60s, and then having literate parents in 80s family planning (i.e. one child policy) which filtered generations of 1-2 kid households where surplus went towards education/tertiary. All the recent highend progress recently was result from that, step by step building on generational phase/timescale. PRC only passed US in total STEM a few years ago, now they on trend to talent inflection point 2x-3x STEM vs US in next 20 years. People mock one child policy, but it was exactly choreographed for this outcome, one of few cases of generational peasant to phd planning, though 50 year foresight to build up greatest high skill demographic dividend in human history, not 100 year foresight because cost is shit TFR in the next 50 years.

It kind of did. GDP per capita grew at around 6% per year from 1952-1980. It was starting from such a low base that it was still pretty low in 1980, but it was much improved. And Mao was not an engineer.

> why had it not taken off before the 2000s?

This topic has been discussed on Chinese forums and social media for like 1 million times. The short answer is it did. To give you a prefect example - the J-10 fighter jet was first tested in 1998, it shot down multiple best EU made fighter jets last year.