Its not rocket science, it really isn't .....
Forums/BBSs own'd by the game run by players,
for players, and modd'd by players... ( free labor )
Server cost and domain name cost these days
should be negligable. Getting 1-2 of those "pricks"
as mods, solves the problem of the trolls.... lol.
Ultimately its the $$.... alot of that is in the data.
Look @ privacy laws now in the EU. The player is
#1, Inno is #2, so sharing with 3rd parties is reduced
when Inno owns/runs the forum/traffic. When Inno
partners with Discord, both Inno and Discord become
#2, and both get all the data. If then, Discord is owned
by ohh say Google... Google now gets direct access to
all the data, bypassing privacy laws, that might/prolly
exsist now with the forum and its current form.
Inno not only saves all the costs for the forum, but Discord
prolly kicks back some greenbacks to Inno.... Sure thats a
win/win for them, but its us players that are the lo-ooo-sers.
Disclaimer:
thats 1 possible, plausable conclusion to the question :
Why is the forum moving to Discord ? Its an opinion, and may or may not be true.