Why did God consider preflood humans evil when he hadnt given them laws yet??

So due to coming back home to my pastor parents for a while, I have to read the Bible and I'm at Genesis 6. I had to flip back and forth a bit cause no where does God tell those humans of the time what exactly he considers right and wrong.

Yes, while they have knowledge on it thanks to eating the fruit, that doesn't stop Him from later on making the 10 commandments and then helping his chosen prophets or whoever to write the books of the Bible. So how exactly could those people know they would be condemned for laws they were breaking when they were never told what those laws even were??

And maybe it's just the version of the Bible I'm reading (NLT) but God never gave the other humans at the time a warning that he would be flooding the earth or to repent or change their ways. He just went 'Damn they're all messed up. Time to reset without warning' LIKE? I would understand if God sent Noah out to be like 'Yo, within the 100 years I'm building this boat, you should probably clean up your act to be righteous with the big man upstairs before he floods everything.' but they got NOTHING.

Maybe there was no hope for them but better I'd prefer to read 'Noah warned them of what was to come but their hearts were filled with too much evilness to listen' than like... Nothing. This is a stupid rant but still.