I think a lot of people don't realise how a subscription service coupled with sell-through alters the financing of game development.
Currently the financial model of game development is like property:
Decide on a budget
Spec the project
Rejig the budget lol
Begin development (e.g. buy land, start core concept outline)
Continue development
At this point all your costs are upfront with no guarantee of a return OR cashflow to keep the project going
At some point you start taking off-plan deposits or, in the case of games, pre-orders. This allows you to gain further funding on the basis you've already locked in x% of your costs as covered in sales.
Ongoing pre-orders can be counted as cashflow to your finance team and presented to shareholders as confidence in the title, allowing people to be paid while continuing to work, project to continue.
Your risk is mitigated, but still there as even with pre-orders if the game is a stinker al your P&L models fall apart, especially when you include post-release monetisation (PRM)
Subscriptions change this by providing ongoing cashflow that is reasonably guaranteed (I'll come on to why this is in a sec), and reduces the reliance on lean times during development followed by a massive influx of cash over a short period of time, which then tails off into PRM which may or may not help you reach the project's profitability target.
Instead you have a constant revenue stream buttressed by sell through purchases and PRM, and while you will still look at P&L per title, so the downside risk of a game underperforming at both retail and PRM is mitigated.
Now - guaranteed cashflow. I see people in this thread talking about how they used the GP trial to get FH4, and how can that work...well, your behaviour isn't typical of people who use subscription services. For most households Netflix is essentially a utility bill rather than a discretionary purchase. Keep your churn rate low by wedging your service like that and you have an income stream that has consumer inertia that mitigates churn risk.
Tl:dr - sub services mitigate the financial risks of gane development by proving steady cashflow and offer the opportunity to convert into permanent sales and PRM.
By positioning the service correctly, you can induce consumer inertia when it comes to cancelling subscriptions, reducing churn.