Its 100% native Objective-C code on the client, plus a mixed Objective-C and Python pipeline for maintenance and backend - around 60 kloc in total. The other major components are a 50 kloc config-file and a 800k row database.
In addition to being fully desktop native, we also don't sell subscriptions.
> why aren't devs making desktop apps any more
we have a unique insight into the market, having seen every Mac app published in the past 20 years. i don't think your assertion is correct, there are a lot of desktop apps around. there are a few thousand apps under active development, and the majority of them are actually native, not electron (we count 25.000 native sparkle-feeds URLs versus 4.400 electron-feeds). i'd phrase the question the other way: why are there still so many native apps when most end users would never spend a dollar on software? i believe there are quite a few hobbyists out there, developing for fun or out of hopes of being able to make a profit later on. that further contributes to the expectance that software needs to be free, further destroying an already very weak market.