I can shed some light on this. Most of these villages began their demise around the middle to late middle of the last century, before or during the upsurge of the economy that would lead to the city's boom times. Times were very tough, especially out in the sticks, so those that could move abroad, or send their kids abroad, did. That is a large part of why you have a huge ex-Hong Kong community in the UK, Canada, Australia, etc. Entire villages cleared out.

The thing is, they moved but most often retained land rights. So those villages fell into disrepair as people moved but the houses and plots of land usually belong to families that have lived abroad for one, two or three generations now. They could be developed but so far there's little incentive for people to do so, despite the high property prices (those that were very successful abroad instead bought property in Hong Kong's new towns and have seen asset values skyrocket).

Hong Kong's government has historically been very good at providing services for the outlying areas. The many villages that did not end up abandoned have for decades had all the amenities, with stable power, clean water, fiberoptic broadband and often gas as well.