Well, you can, you just need to amortize them over like 20-30 years, maybe longer. I mean if you buy a house you don't say you lost $500k that year do you? Plus you still have the asset...just like them.
The acquisition part is the not-straightforward part because it's not all first-party studios who don't have a choice in the matter on how they want to be compensated for joining your subscription.
Publishers need to weigh the fees paid by (in this case) Microsoft against the value of their IP. They don't want to be paid too little for something that might end up being a huge hit... except that half the 'sales' got siphoned off into a subscription deal they made on the cheap. Microsoft likewise doesn't want to pay top dollar for a game that promises the moon and the stars and ends up with <100 player counts a month after launch.
A lot of those titles will
also be licensing content. We're seeing titles go dark because otherwise viable games are tied to a larger franchise and the publisher's contract with $movie/$TVshow/$mediaempire is up, or they licensed music for the in-game radio station, and that license is up and nobody wants to renegotiate or fix it in any other way. Boom, game dies for a stupid reason.
That's before ongoing support costs. Games are less patch-reliant but not zero patch-reliant. There's ongoing server maintenance overhead for online games-- sometimes very little, sometimes significant. Sometimes the old server infrastructure was set up by someone who left 10 years ago and nobody has the know how to rebuild them.
So you may pay to have access to an asset for a period of time, but it's not always exclusive access and that asset depreciates at a highly variable rate. Games usually have a pretty high roll-on, roll-off within the first month or so. Some settle into long-term stable high player counts, some dwindle to a small but still active player base, and some just dwindle down to almost nothing. If you're really unlucky that dwindling takes a few weeks not years...