Get transaction issue


I’m trying to sync with eos mainnet and it works well.
My issue is,
I can get block information with transactions when I use

cleos get block {block-num or block id}
but when I try this,
cleos get transaction {tx-id}
it prints error : transaction can not be found.
But if I use the command with block info like this,
cleos get transaction {tx-id} -b {block-info}
it can be found.

I’m curious the reason why.

Help me whats the problem with it.