I think the impact of wealth and access to nutrition and an environment that does not stunt development plays a major role here as well. A good example of this is height in Europe post-industrial revolution and improvements in medicine:
Most notable being a 20cm increase in the Netherlands in just over 100 years as well as changes in places that industrialised quickly like China:
Not to say that geography plays no role but it’s closer to 10cm gap than a 30cm one.
It’s so incredibly heavy-handed with its plot devices to the point that it feels like its genuinely doing it for “engagement” like you said. I enjoyed the acting by the host couple and could definitely see a good movie in there if it wasn’t for the 2 protagonists’ grating personalities and the combination of tropey and non-sensical descision making.