Here is the Thing with modding at the moment: As long as the Game gets constant updates, Modding doesn't make much sense. As soon as a new update is out, the Mods will break.
The second reason is, nobody really figured out yet how to mod the Game properly. You pointed out official modding tools, but those might only come when Frontier stops supporting the Game.
I don't see the End of the Road for the Game yet. And i hope this Game will get support for some time. After that, your wishes might come true.
So people update their mods or they dont. Also getting a game update (which we hardly get anymore anyway) doesn't mean mods will break. That only happens when something within the game fundamentally changes, not just when they add a new ride or wallset to the game. Unless they are gonna totally overhaul some core functions (and its safe to say they wont anymore at this point) i see no reason why mods would "break the game" or whatever. This also isn't an issue in any other game. And even if they did, a modder usually updates its mod. Especially when its on the workshop.
Cities Skylines gets regular DLC's and it has tons of mods. Every once in a while with a new update, some mods lose their functionality for a few days, untill the author updates it. The workshop is so super easy and convenient with this, it's no issue at all and beats having a game without mods.
I run a server for a game which gets updates every month. And like every once in every 3 months or so, a single mod maybe doesn't work for 1 or 2 days untill the author has updated it. And I got about 50 mods running in total for that game. This isnt' even an issue at all and having mods is worth it 10000x more than.
So yes, maybe if planet coaster had mods and the game gets an update, there is a slight chance that 1 in every 100 mods loses functionality for a few days untill the author has updated it. That's not even remotely an issue whatsoever and i'm surprised many people keep bringing this up as an argument. [haha]
It's safe to say it won't matter for 99% of the time and that 1% of the time that a mod does lose functionality with an update is only a mild temporary inconvenience for a few days untill someone fixes it which they always do.