Why does the founder of Litecoin only advise everyone to buy Bitcoin?

Because all the altcoins in the crypto world are aimed at exchanging for more valuable tokens

For example, exchanging your $BTC btc, $ETH eth, $SOL sol, etc.

Why do they have no faith in their own coins?

Because they know their coins have no consensus, no value, they are just air

SOL
SOLUSDT
122.75
-0.88%
ETH
ETHUSDT
2,947.99
-0.52%
BTC
BTCUSDT
87,667.5
+0.27%