Okay, let's clarify something.
Plex has been essentially "giving away" a service for the better part of what, 20 years?
And that service is the remote proxying of your server and its access. Basically, you didn't need to open a port, expose your server to the public, Plex provided a proxy through which you could stream to your heart's content, knowing that your server is both accessible and (more or less, more than if you managed it yourself in most cases) secure.
Now obviously, they are a company and thus need to make revenue to continue developing the server, clients, and maintaining the infrastructure. Mind you, Plex has 25 million active monthly users... Even if just 10% of that is active at any given moment, streaming at 10Mbps... that's 25 MILLION megabits per sec. 25 thousand gigabits. 25 terabits. PER. SECOND. Being proxied through infra Plex has to pay for. Your average proxy/CDN dataserver unit can do usually around 100 gigabit, meaning Plex needs 250 of those. Just to serve 10% of the userbase.
And don't forget that, unlike "traditional streaming platforms" where CDNs can greatly amplify bandwidth (due to repeating same content to thousands/millions of people), Plex can't easily utilise this infrastructure approach, AND they have to constantly stream INTO the proxy as well as outwards (a CDN pulls in the source file once and then distributes it, Plex literally needs to pull the data stream on-demand, without storing it).
I don't like these restrictions they're putting in, "enshittifying" the service - e.g. if I have my server forwarded properly and don't need to go through their proxy, I should be given a free pass (albeit I already have that since I bought lifetime Plex Pass), but I do get how it would be annoying for the average user to not realise why they're asked to pay when their friend isn't.
Streaming traffic has to go through the Plex proxies if your server isn't exposed to the internet (meaning proper port forwarding, no CG-NAT and no other ISP fuckery that would prevent such functionality).
Of the 25 million users of Plex, how many do you think have the setup (either the ability or availability) that supports direct playback remotely?
Ideally yes, only basic things like authentication and server mapping should go through the main Plex servers but sadly this isn't the case. And Plex has provided that service for years, for free. Them asking money for a service that isn't free to run, is fair game.
What isn't fair is how they've been doing it.