It couldn't be more obvious and intuitive that the people you're around for half your waking time would be one of the bigger sources of potential partners, and also just friends/acquaintances where a partner comes from the social networks thusly formed.
This paper suggests meeting people directly or indirectly via work was second to meeting through friends around the turn of the century, though there was a wide spread of how people met so it only amounted to a fifth of couples. Then online took over....
From the HR training i got from many places, harassment is what gets you in trouble with HR i.e. persisting after your advances have been rejected. Politely shooting your shot is fine, unless the target reports to you.
You're missing the distinction. I met my wife at work but any and all propositioning happened outside the office, and not at office social events either.
Uh, only if invited? I mean do you not ever get lunch with coworkers or invite them to events you're hosting or ask if they want to see a movie or concert with you that you've been into? The important thing is to establish a positive social relationship before indicating any sort of sexual interest, so they know you as "My chill coworker John" rather than "John the guy at the office who's always staring at my tits and asked me out for 'drinks' before we ever had a single conversation." It's not impossible to establish sexual or romantic chemistry before establishing social chemistry, but it's sure harder.