LOL. Underpowered? Can netbooks edit 4K videos?
...but can the 12" MB usefully edit 4k video? There's a difference between being technically capable of something and actually being any use for the job. Apart from the processor and small display
The original Netbooks weren't supposed to edit video (let alone 4k! In 2008?) - they were designed to be cheap, ultra small and light and adequate for email, web browsing, wordprocessing, casual gaming etc. The comparisons between the Air and Netbooks were always ridiculous - the Air always had a far better, near-full-sized keyboard, better display, reasonably powerful processor c.f. any "netbook" and, rather importantly, literally cost ten times as much. (MacBook Air intro price: $3098 - Asus eeePC: $300).
I think there's a whole slew of reasons why Netbooks died out - but I suspect mainly the industry doesn't want to sell you a sub-$300 computer when the could sell you a $500 tablet or a $700 PC laptop. Microsoft was partly responsible for 'dumping' low cost Windows XP licenses on the netbook market to kill off Linux - which forced makers to increase processor, storage and RAM to cope with XP's requirements... but then Asus et. al. spared every expense when it came to making Linux work well on small screens, and also kept invoking a deadly combination of underestimating demand and invoking the Osbourne effect - there always seemed to be a new, better eeePC announced before anybody had the previous version in stock... pretty soon "netbooks" were just entry-level (if not higher) laptops.
Interestingly, Chromebooks (the new incarnation of Netbooks) seem to be heading in the same direction - I recently needed to buy a low-end Chromebook to test stuff and all the sub-£200 models are quite old (although I did end up with one that provides a perfectly servicable 'web terminal' with a half-decent keyboard for £160) - the newer ones are significantly more expensive, with the Google Pixel Book costing the thick end of £1000.
As for the 12" Macbook - I just feel that it was "neither fish nor fowl" - too expensive for a web/office-only 'second laptop', not powerful enough for a 'main laptop' and not that much more portable than an Air.