"Dromund Kaas. I want to see what has become of it myself." At one point it not only held the Sith Academy but also was the imperial Capital.

And Darth Malgus' homeworld but that was of little interest. He planned on piecing together the full picture of the fall and re-emergence of the Sith for himself before reaching out to the current members of the order.

And well, the Jedi has been helpful so far. Neither of them really had an order anymore. Not really. Malgus didn't know the current Sith, he couldn't just walk back into the picture. He knew it wouldn't be so easy.

Jedi also rarely double cross, and with having no allies, he's have to make do with this one. Even if he hated it.