I think OP is talking about new posts rather than new threads on existing posts. Although I'm still inclined to suspect that spam mitigation factors¹ caught their particular post rather than this being a general thing, because I'm pretty sure I have seen brand new accounts post interesting stuff.

Seems like OP's nose is just out of joint because their terribly important post got clobbered :shrug:

¹ Which is not to accuse them of posting spam - just that it scored high on some metric or other.