It's not hard to notice whether an element has focused, and especially if you know you have flaky hardware, be aware of that.
All your other reasons are the fault of the website, not the browser.
I expect the text actions (input and editing) to work on text. If I have to think about which possible, implicit mode I'm operating in, it's a bad design.
You're implying that the computer somehow magically (telepathically?) determines exactly where your input is to go. That's not possible.
Or are you saying that before every keypress you visually verify where your cursor is, is it blinking, is the right window focused, are there multiple cursors with fake focus, etc?
In a word, yes. It's seriously not hard to see where the focus is. I usually have multiple windows open but there is only one cursor and it's the only thing that's blinking. Many others I've seen maximise their browser window, so there shouldn't be other cursors much less blinking ones visible (unless there is some strange bug which does cause this --- in which case that is definitely a bug to be fixed). If I'm at all unsure, I make sure.
Besides, if I'm going to submit some very long text, I'll write it all in a real text editor first and then copy-paste.
I don't always look at the screen either.
That's like saying "I don't always look at where I'm going when I drive. Why do I keep crashing into things?"