Are only two new train sets available in August 2018?
Those are the two City-themed trains that are currently available. LEGO is currently transitioning to a new electrical system for trains, so that may explain the relatively low number of trains available. There are a couple of other trains available if you are interested in something outside of the City theme.

There's Winter Holiday Train (10254):



And also the new Hogwart's Express(75955) (currently backordered):



These are just the sets currently available directly from TLG. LEGO has produced many, many trains over the years. You can find out-of-production train sets on secondary markets such as Bricklink or eBay.