You can consider it so theoretically, but for many teams, especially small teams, OS-level systems admin is a different skillset and non-trivial burden that they are glad to pay a premium for, which is why offerings like heroku are successful.
It may work that way for you, but it definitely does not for many many teams.
"You already have to walk to the store, so hiking the appalachian trail is just another part of your walking strategy" -- this is an exageration, the difference between walking to the store and hiking the trail is probably larger than adding OS-level maintenance, but it shows "you already have to do X so doing anything else that I can also call 'X' should be trivial" is a flawed form of analysis, it tells us nothing that you can call all of it "walking" or all of it "patching strategy".
This is "you'll always have to do X, so might as well do 10x" argument...
Just because I have to manage patches for 'my app and it's libraries' doesn't mean also handling the OS and everything else that would already be covered by the serverless service is no biggie...
If you're doing a toy demo app, or a website for your local flower shop, yes...
Any non trivial company's systems are not just some random container with a "Nodejs app" inside. They need to keep state, handle caching, redundancy, global CDNs, and lots of other layers.
You either build all those and full ops on top of containers (or whatever), or you get them off the selves and ready to play with a serveless service and their state solution, plug-and-play ready-to-use caching layer, and so on...
If this were the reason to use Serverless, it doesn't buy you much. Ports? You set that up once and you're done forever. OS patching? You already have to manage patches for your app and its libraries, so OS (really container) patching is just another part of your patching strategy.
The reasons to use Serverless is the same as everything else in the cloud: 1) fast scaling, 2) sometimes it is cheaper depending on X, and finally 3) you don't have to think about where to run it.