How can a game that relies on 3rd party tools to operate also not encourage thier use.

Web-based content you access through your browser/standalone programs and client-based addons/overlays are entirely different.

If the likes of trade macro's, Path of Building etc were to disappear tomorrow

The trade macro is an explicit exception GGG has intentionally made. Chat automation like this is allowed.

Path of Building is a standalone tool that Doesn't interact with the client. And it's arguably done more harm than good to the game, over the years. It's encouraged the whole spreadsheet warrior mentality of optimizing everything to a pretty crazy point. If it had never existed in the first place, it's arguable that the game might be in a healthier place.

As Chris says, GGG doesn't outright ban 3rd party tools. They won't promote them, because they're not developed in house, and that opens up all sorts of liabilities. There's a difference.