game prices don't completely cover the cost of development and definitely don't cover server operation costs every month.

Nope. while it might be true for small independent game developers it's totally false for big company, like MS just a fifth of the profit they paid to shareholders is enough to run good server for like five years

Games from big companies, except the games that went flop, or F2P games, or the game that purposefully sell at low price in order to sell other forms of microtransactions, then most games are profitable

they don't have to rely on monthly subscription to be profitable but the problem for them is "the profit is not high enough" and that's why they do this