What the big platforms have done is eliminate friction at all the critical parts, to make it easy for users to onboard, easy to share, easy to grow within the platform, and of course hard to leave.
I've been thinking about a low cost but not free platform too. If it ever happens, it will have to be AT LEAST as frictionless and enticing as the existing platforms. The table stakes are very high. Since cost in of itself is a source of friction, that means the rest of the platform needs to be even MORE frictionless.