If you haven't noticed this game hasn't got much besides reskinned content since adoulin released and even with that they are frugal. Costs of this game can't be significantly higher than electricity.
Price for standard subscription maybe didn't go up but workload for sure didn't either.
I'd get you coming from if it wasn't a multi million (or is it billion?) stock company we are talking about.
Additions are irrelevant (even thought they are adding adding stuff), the costs involved in upkeep are enough to justify increases due to inflation. You're not really paying more than you did 15 years ago if you get wardrobes, you're paying the same amount with a bigger number. If you don't have any, you're paying much less.
90+% of the cost of every video game is spent on wages, when a company says they spend 100 million making a game that almost all went on wages.
Wages = developers, server staff, customer support, GM staff etc (even if you think they suck, they still have to exist in those roles for the game to run and still have to be paid, and SE pay above the norm across the company) Plus they need staff for each region the game runs in, Japan, EU, NA.