Yes, this happened very early on with Bitcoin. Casinos where every wager was a transaction. Then some started actively just spamming.

It led to the transaction pricing mechanism. Every transaction includes a bid on how much you'll pay to have it included in the chain. Miners pick the highest bids from recently broadcast transactions. There's no requirement to do so but it's economically incentivized, as the miner receives the transaction fee. Any sustained attack becomes very expensive. And other users can still pay the asking price to get their transaction in the next few blocks.

Bitcoin has in practice maxed out the great majority of blocks (about 1 MB per 10 minutes) for a while now, and so many cheap transactions just never get processed as they're always outbid.

That happened on Ethereum with a game called exit.scam where the last person who buys a token wins, but every time someone buys one the timer resets. In order to win the game a bunch of miners colluded to make it impossible to get a transaction through, guaranteeing they bought the last one.

This has basically already occurred IIRC - the entire bitcoin blockchain is now too massive for most people to entirely download and authenticate; most people rely on exchanges, etc to do it for them.

I did this to namecoin for fun with a bash script for 36 hours in a loop once. This is a true story. Back in the merge mining days they gave them out for free and no one knew what to do with them.

I took all the public namecoin addresses I could find and put them in a text file and sent everyone dust. Fun times.