Player Investment

If you want to keep players around for more than two sessions, you must find ways to get players to invest in a game beyond just imagination and hours.

Personally, I find option 5 ineffective, but it's popular.

D6

1. Charge them money, either a full subscription amount up front for a specific number of sessions or a few dollars to pay for the next session at the end of each session.
2. Have them sign an oath with consequences if they fail to attend every other week, on time.
3. Send them photos of their pet being hand-fed by YOUR HAND in YOUR YARD along with a note reminding them to keep a log about the next session.
4. Pay them money and make them an iron-on T-shirt with your campaign logo on it.
5. Provide a meal and/or drugs (alcohol counts) with the game.
6. Require that they buy gaming materials. They have to own their own dice, at minimum. Depending on the game/setting/etc your are playing, you might be able to add more things.

Alternately, host a Breakfast & Dragons experience on AirB&B. Require a six-night stay for campaigns or accept that you will only be running one-shots to completely avoid the problem of long-term player investment.