Another thought though is that some of the pay-to-unlock (e.g. weapons shortcuts, or vehicle shortcuts) are born by people's sense of entitlement these days - want to see everything, but without working towards it (whereas I get a sense of achievement when I have "unlocked" something through progression)
Could not disagree more, it's hardly a shocker that people want access to he stuff they have paid for, they are born of greed by the devs, the awful mobile gaming scene and games being developed with 'as a service' being at the top of the design tree.
It's like going to the cinema and not getting the ending of the film because you haven't spent enough time in the cinema.
Progression, progression, progression is all anyone talks about and yet all I see is people getting stuff for playing longer, that isn't progression its just yet more of this incessant loot culture that's infected games for years and the basis upon the awful loot box system is based upon.
Skill, map design and a fair playing field should be enough to keep anyone engaged as it should be fun and that in itself should keep people engaged, unfortunately grinding, unlocks, levelling up and loot drops seem to have masked much of that and the community seems to have not noticed.
However I am old, I am an ex Q3 and UT99 player and perhaps just haven't lowered my standards enough yet to think that any of these systems actually add anything worthwhile to the game.