How do you keep players from dropping off during midgame progression in an idle or incremental game on Kongregate, especially when the resource curve starts to slow down?

One good way is to add small but steady goals that give players something to look forward to during slower parts of the game. You can introduce short challenges or rotating boosts that make the midgame feel more alive. It also helps to use predictable schedules the same way a service like https://affordablewastemanagement.co.uk/
follows clear routes and timing. Players like when rewards come at moments they can understand and expect. Another trick is to let players unlock tiny bits of story or art as they wait. This keeps the pacing soft and pleasant instead of empty. You can also give players choices that change the speed of growth so they feel more in control. If you watch player data and adjust the curve gently you will notice engagement becomes more stable.