Gamification is good to initially gather a community but eventually you supposely want millions users in your platform and gamification isn't enough of course
No it is true. To get millions of users you need to deliver a honest, seamless, and accessible product, being accessible, very transaprent, and with a charismatic team.
to have millions of users, first of all it serves an aggressive and targeted advertising campaign that reaches many people interested in the service, and offers unique features that any users can not find from other similar services...
keeping users indeed takes constant improvement and maintaining of your product. Attracting the users you can manage through hype and marketing.