Actually they'd need both.
And companies are not so dumb as not to understand this. Any company that started charging or went into a subscription model, offered both excuses and justifications for doing so.
You might be think "it's a free country, it's their product, and they can do anything with it".
Which is true in a trivial way (they're allowed by the law to do anything they like in that area), but it's also wrong.
Wrong in that in practice they're not really free: to survive they are bound to the market and their customers responses.
So they're free only as much as they're OK with pissing their user base and potentially losing sales (or have most of them go for some other product, and kill their own user base -- e.g. Quark xPress vs Adobe Indesign, and tons of other similar examples).
If the problem is access to files, then they could just have a free converter tool to some standard format.
If they started charging just for use they wouldn't need neither an excuse nor a justification.
I really don't see your point.
If you could explain further why you think sublime would need an excuse for charging a monthly fee I would really appreciate.