Open alpha testing of the 5.0 HD mod (online lobby).

You've confused the concepts of a PRODUCT and a SERVICE.
A product can be paid for once and taken away forever (and even then it might eventually break, and you'll go buy a new one).
Services are paid for over and over again in each specific instance of providing the service.
Internet, hair salons, booster rides at an amusement park, utilities (gas, water, heat). You can argue about prices, but the nature of a service and a product is different.
Or try to come up with what the price of a "lifetime subscription" for the lobby should be and why. And what will you do then if only you pay it, others don't give a damn even about the monthly one, and baratorch also gives up on the whole project. These are unsolvable issues in the case of a service.

As far as I remember the chronology, HotA first had OX, and only then did the lobby appear. That is, lobbies for OX are not fundamentally important. The lobby isn't critical for me; playing via Hamachi is fine too. If there were something like a "key" as in Warcraft/Diablo that would allow one to host themselves with OX, for example, while others couldn't (because they didn't pay) — I would be satisfied with that. That's why I believe the possibility of purchase exists. Correct me if I'm wrong, but so far logic suggests it is so.

Added after 6 minutes

I cannot make a lifetime subscription. I simply don't imagine what price tag I should set. Although there is an option that is easy to arrive at: 3,5 million must be divided by the number of people ready to buy a "lifetime" subscription.

Thank you for the answer, I'll keep it in mind. I will hope that after paying for a few months, some number of people will eventually come to the same idea regarding their willingness to shell out a sufficient amount once. My apologies for pestering; I just wanted to finally see an answer to my question. I am satisfied with the answer.