Short answer
Because nothing supports the price once attention moves on. Early holders sell, new buyers dry up, and with no revenue or product there's no floor.
A memecoin's price is set by the balance of buyers and sellers in its liquidity pool. In the first hours, buyers often outnumber sellers. As the token gets older, early buyers and insiders take profit, and there are fewer new people arriving to absorb that selling.
Add the sheer number of new tokens launched every day, and attention is the scarcest resource. When it leaves, the chart drifts down until trading mostly stops. Some tokens are also deliberately drained in a rug pull.
This is why we repeat it everywhere: memecoins are high risk and can go to zero. Past results don't predict future ones. Only trade what you can afford to lose.
See the checks for yourself
18+ only. Self-custodial: you keep your keys. 0.5% per trade, no minimum. Memecoins can go to zero.