But we (and other animals) don’t just fall asleep involuntarily? We do decide to (go to) sleep. I know I missed your question with this take.
Maybe it’s a bit like when we try to focus to learn something. We have to create a situation which supports that desired brain activity, and control our attention. In both cases, we want to minimize distractions.
So I guess one answer to your question is: Because sleep is not a simple activity like watching TV or riding a bike, which we could switch to in an instant. Sleep is a state of mind (and much more physiologically), which requires a certain environment, relaxation and time to transition.
A related question might be, are there people who can deliberately make themselves sleep? For example, those that can close their eyes and just sleep in seconds. Are they falling asleep, but just faster than most, or do they decide to sleep?
You know, this is a good question.
Googling it would ruin the fun, but I’d assume that it’s an evolutionary thing so you don’t decide to go to sleep in an unsafe situation and get yourself eaten.
I bet you’re right. It also probably has to do with shutting down/pausing brain function to enter our “sleep mode”. Though I have no clue what I’m talking about so take it with a grain of salt
After a quick google myself, it looks like this is basically it. There wasn’t a whole lot of info but from what I could find our body needs a way to make sure we don’t do something stupid like sleep while standing up or in danger. This means it’s up to our body to let us sleep rather than letting our consciousness decide.