In general, Yamaha doesn't include MIDI DIN ports on their less-expensive consumer-oriented (i.e., home use) keyboards any more, but they do have MIDI DIN ports on keyboards aimed more at professional keyboardists. For instance, the PSR-S775 and higher models have MIDI DIN ports, but the less-expensive PSR-S670 and lower models have USB-MIDI only; but the inexpensive MX synths do have MIDI DIN ports, because they're aimed at professional keyboardists more than at home keyboardists.
Whatever the reasons might be, it's actually very simple to route MIDI between two PSR-E433 keyboards using their USB-MIDI connections-- that is, if you're connecting both of them to a computer or laptop. I've got four Yamaha keyboards now, and that's how I do it. I used to keep my PSR-E433 and PSR-E443 connected to my desktop computer all the time, and would connect my YPT-400 (a.k.a. PSR-E403) if I ever wanted to use three at once. But with my current arrangement, I've got just my new PSR-EW400 connected, and my other three are stored away due to limited space.
If you need to connect two USB-MIDI keyboards in a situation where it's inconvenient or undesirable to use a computer or laptop as a go-between (USB host and MIDI router), then the iConnectivity mio4 or the Sevilla Soft UHMR might be just what you need.