JF, you took control of a region without any resistance and was uncontested during such action. Invading an empty region like that would not be challenging for anyone but allowing such open/free regions in the game does unbalance things for everyone especially when it occurs early on (turn 6 was WA's last orders so there was no opposition at all during your conquest).
The act of spending gold/orders doesn't justify the acquisition of having open/free regions in the game. I waste gold/orders all the time

, it doesn't mean that I deserve to have free pc's without a player being around to oppose me because that ruins the game for everyone else. It's fairly common for a player to plan on invading a region, spend the necessary gold/orders to prepare, then suddenly get invaded by others causing one to go on the defensive changing things for them.
That's not wasted gold/orders, just a normal risk in the game. Such expense for planning an invasion that didn't prove fruitful is just one of the risks in the game. That condition is always present but such expenditure of gold/orders does not justify allowing open/free regions in the game which ends up ruining things for the other players. This is why destroying pc's for dropped positions is necessary to prevent such a vacuum in the game.
You've mentioned that you or others would quit if pc's were removed after gold/orders were spent trying to acquire the region but many of us have been in games where our initial plans of conquest was interrupted by others and didn't quit because of it. Players adjust and move on rather than drop out if they had spent gold/orders that didn't prove fruitful towards their original plans.
So quitting under such circumstances may be your opinion (which is fine) but I haven't seen that occurring in games so far. As an example, in games where pillage/meteor storms were rampant, pc's disappeared like crazy and caused wasted gold/orders for many of us when moving emissaries/groups/agents around the map but that didn't cause players to drop out. Instead, players continued on and such games ended up having an interesting twist that were more exciting and challenging than otherwise.
Handling dropped positions by removing pc's from the game is important to eliminate the unbalancing effect of having open/free regions in the game. If it helps, just consider starting a new game where a neighbor has an open and uncontested region next to them that others are too busy or in battle to contest. Would that really be fair to everyone in the game? Certainly not, so that is why the game needs to have a mechanic in place to remove pc's for dropped positions and remove such open/free regions in the game.
Though I am a bit curious as to why you dropped out on turn 20. You had the commanding lead in status points, control of 3 regions, tried to declare victory, then just dropped out. If you can't state the reason on the forum, please send your thoughts to support because I really thought you would win that game.