I come with a questions that I can’t seem to articulate well enough to find a answers on YouTube or google. Hopefully someone understands what I’m asking.

So I’m wondering what’s to stop someone from trying to guess the 12 word seed phase of a large account. My understanding is the account is public and the 12 word phase is not. But If the blockchain is transparent and we know what BTC is where why wouldn’t people set up algorithms that constantly guessed 1000 different 12 word phrases a second till they eventually got a hit. Also what’s to stop someone from setting up something that constantly generates empty accounts to eventually lock out a bunch of different seed phase options? I get over the course of a day or week it might not be fruitful, but over the course of a year or many years wouldn’t you eventually guess the 12 words if a computer(or multiple computers) are constantly guessing 1000 guesses a second?
My understanding of BTC and self custody is very limited and I’m just trying to understand these things.