Yes, Resigning is part of the game

You are wrong actually. Players around 1200 and below, when they lose their queen, there is still a little chance winning. I won’t talk about players above 1500 though. But you didn’t specify the fact that players under 1200 still have little chance. Also “If your opponent has three queens vs your lone king and you won't resign, you are being a bad sport” —Nope actually. There is still chance of stalemate. Yes it is rarely, but still there is a chance.

It's been part of the etiquette of the game for decades and it's even mentioned in The Queens Gambit when Beth Harmon is learning the game. Rating has nothing to do with it.
It’s up to you to resign or not. Stalling is the bad sportsmanship though. Rating does make a difference actually. If you said a 300 rated players loses his queen, he might get it back.

How’s about you prove your skill to convert instead of expecting a free win just because you have a material/positional edge. I don’t know you, I don’t know how good you are, I may not trust your skills to convert, either. Deal with it.

“Insulting your opponent by implicitly stating that you don’t think they can actually win.” You see… I actually do believe that they can’t win it. If you’re 10 moves into an advantage and I still see no path or plan for you despite you being up plenty of material, I’m definitely playing on.
Queen blunders aren’t the end of the world especially if you didn’t lose anything else. Instead of complaining here, win the game…

You're completely wrong. You can resign or not when you want to. You can't force anyone to resign. Cry about it.
Why is it that in the countless threads where an op rants about their opinion about resigning do they never specify anything about time control or rating or really any other context?
Seeing that it really. really matters. Is it one of those things that people who think their opinion is objective truth tend to not be all that great at recognizing nuance?

It's been part of the etiquette of the game for decades and it's even mentioned in The Queens Gambit when Beth Harmon is learning the game. Rating has nothing to do with it.
Interesting fact that some may not know: in the Romantic Era of chess (1700s to mid-1800s), it was considered poor sportsmanship to resign in a lost position.
You were expected to play on, if losing, to allow the winning player the glory of fulfilling his well-earned checkmate.
Only cowards, and spiteful players, chose to resign. A true gentleman played on, and graciously allowed his opponent the satisfaction (and the showmanship) of completing the win.

There are two issues here.
1) If a player has promoted multiple extra queens then the opponent has a very realistic chance for a stalemate. As a TD (arbiter) my rule of thumb for games with new players is that a K+Q vs K is a draw 50% of the time and a K+2Q vs K is a draw 90% of the time.
2) The OP is (currently) in the Crystal division and getting points for moving up requires winning a lot of games, preferably ones that finish quickly. There can be issues when somebody that wants a quick win is playing against somebody that wants to play out the game.
Seeing you lost there was better than a zero chance of their winning, no?
Increment is a thing.
1) If a player has promoted multiple extra queens then the opponent has a very realistic chance for a stalemate. As a TD (arbiter) my rule of thumb for games with new players is that a K+Q vs K is a draw 50% of the time and a K+2Q vs K is a draw 90% of the time.
There is also that someone that promotes extra queens rather than just executing a simple checkmate has no business complaining about someone else's bad sportsmanship.

Allow me to introduce you to Magnus Carlsen
Magnus got thoroughly outplayed.
No chance of him winning (King+ bishop vs. King+Bishop+3 pawns). But he played on for the flag, regardless.
Magnus is notorious for not resigning in worse positions. He's the kind of player who will play on with just a king vs your whole army, just to make you work for it.