Because they don’t want you to host things at your house, even though that’s perfectly fine from a technical standpoint. They might want to sell you a “business” line for this, or they just don’t want the traffic (since at least in my area, traffic is always included in any home Internet connection).

Let me put it this way: I don’t own a car.

I do own 3 bikes: normal, electric, electric-cargo. Train gets used for everything else. Tram within my city, but the city is small enough that I can reach most of it by bike (say up to 10km). Intercity (or equivalent) for cross-country journeys. Usually that’s faster than going by car anyway, and I don’t have to actively drive but can watch a movie or play games or whatever.

it’s barely December. Who even thinks of wrapping presents now?

Movies generally have a much longer production time than a year. So the script was most certainly finished before ST III was released in cinemas. So BTTF writers would only have knowledge of ST III if they also wrote it, and even then it’s highly unlikely that at the time of writing BTTF it would’ve been public knowledge (or even a made decision) Lloyd would be in ST. Getting most certainly wouldn’t have even started for BTTF.

Like others have asked, we’re missinga lot of details on what you mean by tag system. What’s the origin of a tag? Just a text field with free text (maybe assuming comma separation)? Are available tags defined per instance? Per community? Globally? And consequently, who maintains the list? One tag or many per post? Per comment?

Can I tag other peoples post or comment?

You seem to have a reasonably concrete idea, but unfortunately I don’t yet, so it’s hard to answer.