It probably isn't legal. But who is going to pay for the fight to stop it? Mom & pop who have had their home connection used? A class action that no one but the lawyers really win anything from? The fact that most of the projects involved are in jurisdictions that make the legal process more complicated and more expensive, or jurisdictions that simply don't care as long as it is affecting other countries and not them (coughChinacoughRussiacoughcough*)?

What the market will bare doesn't just apply to product pricing.

And someone clicking through a EULA might be an argument for them having invited the use of their resources by a very similar argument to that many used to justify using other people's WiFi back when that was gloriously insecure most of the time ("but the AP broadcast its existence, effectively inviting me to join, and happily gave me an IP address to work with, how could I not believe I was welcome to use it?").

I am an administrator on a forum that was attacked heavily by these "residential proxy services"; most of the time the users have agreed to a hidden EULA somewhere like at installation time of the extension buried deep within.

But almost everyone "a reasonable person" would not recognise or understand the technical words used in the disclaimer, nor even read all the way down where it's buried several links in.