There's a lot more logistics to it than that.
Scoliosis Jones
put it pretty well in the speculation thread:
It's not just editing trailers together. You need to be in contact with partners, have time tables, release schedules and pipelines you can count on, and coordination with everyone involved in marketing for regions across the world. Covid-19 has mucked around with all of that and makes the situation extremely fluid, and Nintendo is a careful company: They don't like showing things unless they feel 100% positive they can show it off and release it when they say they will. They're a prideful company that values their trade secrets, and whenever they delay a game or show something off ahead of time, it's only really ever for major projects that need it, of which we already know what their major game at the moment is: BotW 2. Who knows how far along that is as well. Could be early next year, could be early 2022: We don't know, and without fully knowing what's going on on their end, it's a little difficult for me to say "They should just do this" when honestly, none of us are experienced in running a company or are privy to the internal affairs of what's going on at the moment. Covid clearly hit them hard, and given it wasn't exactly something they could have known about or prepared for, I personally am not holding their release slate this year against them.
Things are hard right now for everyone.