but frontier just confronted the playerbase (the backers) with the decision to either pay for it with a subscription fee or go without. anyhow, they chose not to pay. don't ask.
Not quite - it was never offered as an option. I'm pretty sure they had the networking model all set out long before the Kickstarter ... sadly it didn't work as well over the entire internet as it did in their labs, though they managed to get a fair bit of it fixed up by 2.2.
The funding model bit they did change was a move from the original kickstarter "cash for credits" to "cash for cosmetics". Given their total inability to keep control of credit earnings, that was probably a good decision all round.
handling real-time player interactions with simulation of physics in a 6dof combat scenario is hard and costly proportionally to the complexity of the simulation, the volume of information per player and the number of players taking part. there are obvious practical limits to this, and it requires a dedicated network of servers to run. this is a significant cost that many multiplayer games (even f2p ones) just assume as part of the cost of operations,
To add to this, the big issue for Elite Dangerous - as compared to most other games - is scale.
If there's one player in a RES, the game simulation needs to handle the player, several NPCs, hundreds of asteroids and munitions and fragments. Adding an extra player or two to that isn't a big extra deal, though - more network bandwidth, but that's not a big blocker.
But because the Elite Dangerous game world is so large, the average number of players per instance is 1 (median, mode, and mean to within rounding error). So they basically need one full instance simulation per player. That's a
lot of hardware - fine if it's distributed throughout all our houses, very expensive if they're running tens of thousands of CPUs constantly to keep up with players.
The games with a client-server model are generally designed to have the average number of players per instance be high ... which means a very small game world (by ED standards, anyway), which means no exploration as a profession.
It's basically not worth them switching to a client-server model for the tiny minority of cases where it would be better, when it would be more expensive ... and less good, because of things like input lag, higher bandwidth requirements, etc. ... for the ultra-common case of "a player, on their own in an instance"