All games included in PS+ or PSNow are also in the PSN store and can be buyed.
Devs aren't forced to include their games in PS Plus/PS Now: as happens in GP and since before GP did it, the platform holder and the publisher agree a deal for some games to be included in the subscription. For some games they have a deal, for other games one of them doesn't want so the game isn't included.
There is nothing negative on offering a short time limited trial of the AAA games -which doesn't require any work or cost for the publishers- to higher payers, a small subset of the whole userbase, to encourage sales among them.
Sony is "forcing" them to get extra game sales from their best customers, they must be super worried about i. Guillemot and Kotick must be crying.