At the same time we got a war that lasted far longer than it had any right too. So it's not the only sin on our list for psuedo-retro sci-fi somethings. We decided that things would need to be adjusted to account for multiple nullified factors created in this world. And it was done.

Which is not to say that you're wrong. China did complete research into transistors (ECGs) on their own. But in this world it really comes down to what the relevant parties had in mind or where they were going. Jet aircraft, rockets, or advancing computer sciences may not have seemed relevant to anyone before the 70's. And the wider global effects of war sweeping the international community we could tag it under the lampshade that is labeled "handicapping everything".