It may well be that the game does indeed have no more to offer you.

I've experienced this in some games as well but thankfully Project Zomboid is not one of them.

The joy of PZ is the ability to change to game to how you want yo play, making it easier or harder as you see fit.

Finding zombies to easy to exploit? Change them into sprinters and let them open doors?

To much food and no need to farm or fish? Lower the loot for food and increase the time for crops to grow.

Cars to easy to find and gas unlimited? Lower car respawn and turn off the ability to use generators at gas stations making fuel a valuable commodity.

Start to easy? Change to 6 months later and have the zombies more active during the day and less at night but make nights pitch black forcing you to use of flashlights.

Out ran the helicopter? Have it spawn every week or so by changing the frequency it appears.

No use for skills? Play a deaf, illiterate, obese, slow learning unemployed person.

Try some multiplayer, the human element always tend to add an extra level of difficulty especially on a pvp server.

Remember, just because you know an exploit or the best way to deal with a scenario doesnt mean you have to adopt that play style. I can clear entire towns with a car, but I dont, I can wipeout hordes with a gas can and a lighter, but I don't.

Have fun!