So you're not even paying for Sea of Thieves at all, but you're here in a thread complaining that they're going to sell cosmetic items, as they've said they would from day 1?
If you are paying regularly recurring subscription service fees, you are essentially "renting" SoT and "renting" server bandwidth.
This means yes, subscribers are putting revenue back into Rare/Microsoft.
For example, Netflix subscription fees collected are not all kept as income, Netflix in turn must pay the production companies & content providers a portion of collected proceeds, likely in proportion to the amount content was consumed.
In the short term, someone who buys the game will put an initial chunk of revenue directly into Rare. Over longer terms, a subscriber will eventually exceed the revenue of a one-time purchase, due to ongoing royalty accumulation.
No one plays for free.
I've seen plenty of games go down the "monetization progression".
-Honeymoon: Everything is free & dandy, c'mon in and get hooked.
-Monetization: "Aha everyone is hooked! Let's start charging for stuff."
-Abuse: "Charging for ALL the things". Now to maintain a competitive edge, players who make app purchased hold an edge over those who dont P2W vs. F2P
-Decay: *skulking away in dark if night, muttering, croaking, rasping.... "Rare.... I'm gonna get you Rare....... $10 for a 2x range Legendary EoR, $15 for a vibrating MetalDetector shovel." muttering muttering
Games today need to decide how long they want their DNA telomeres to stretch. Do I want a long reaching game with longevity but modest revenue? Or burn out quickly by getting at that player revenue now, now, now!!