People use slipstream because they don't know how to use their own node. They will pick up your transaction if it's economicly feasible whether you send directly or not. They did get into the blockchain. Or could at least. The truth is there's not much point to large OP returns so people don't do them. It costs a lot to put data on Bitcoin. It's the most expensive database ever and poorly optimized to distribute large bits of data. It's not that people couldn't do it. It's that there was no incentive to do it in the first place. Almost like fee rate is Bitcoins spam prevention and not filters...