1) If it’s a tourney, have the buy-in low enough that you can allow rebuys, and it doesn’t add up to too much money for those who do.
2) Ditto for tourneys, offer an add-on after 1.5-2 hours so people who get short can last longer.
3) When I ran tourneys, I had a points system, and also reserved a small amount out of every prize pool for a future “bigger” tourney which occurred twice per year. To qualify for the special tourney, you had to have played at least 50% of the games in that cycle. Also, players in the special event got bonuses to their starting stacks based on their performance in that cycle. (If you placed 1/2/3 in any given game, you got extra chips for the special tourney). The buy-in was the same as always, but the reserved money from the previous games in the cycle was added on top as an overlay. So taken all together this created an incentive (a) to show up regularly to qualify and amass bonus chips, and (b) to play for a bigger prize twice a year.
4) Bounty chips sometimes help to spread money in tourneys around to more players. Typically, the winner will have the most bounties. But for someone who doesn’t cash, getting a small about back because they earned a bounty or two before busting helps lessen the blow.
5) Whether you switch to cash or not, maybe lower the game frequency to twice a month or once a month, so that it is more special for people.
6) Consider adding some fun incentives like a high hand jackpot which can give hope to the lower-performing players. This can either be made hard to achieve (quads+ using two cards) so that it builds up pretty big over multiple games, or just the highest hand of the night.