If you use a garbage collector, you don't have to do manual memory management, which is amazing for security. You also don't need to worry about buffer overflows and weird pointer exploits.
If you use web tech, you get a lot of important stuff, like sandboxing, handling of esoteric keyboards, RTL languages and screen reader accessibility almost for free. If you use some extremely fast, small and lightweight GUI framework, you will probably not implement those, as they seem boring, and who needs that anyways.
If you go the handcrafted, lightweight and fast route, you're sacrificing a lot of features, possibly without even being aware of what you lose until it's too late.
I will happily shelve a few more bucks for RAM and wait a few more seconds to get an accessible, secure Messenger, instead of one that is going to steal my bank details the moment some stranger sends me a malicious GIF.