I believe that the issue comes about because probably the vast majority of low end arranger users don't even have a second keyboard to hook it to (they are not buying the BOTL if they can afford or need the TOTL!), and due to the primitive MIDI capabilities of these arrangers, you couldn't do very much of any use with them even if there WERE MIDI ports.

These things are designed, marketed, and intended to be used as the sole keyboard in a 'home' environment, for personal entertainment purposes, NOT as one of many devices in a 'pro' gigging rig...

But my main peeve remains that, although higher end arrangers DO have MIDI ports, their OS's are VERY poorly designed for the purposes that those MIDI ports imply... The control of external gear, or the ability to be controlled by the same.

Let's look at the two main scenarios that having MIDI ports might encourage you to try...

First is using a module, as an extension to the tone palette of your arranger. What we are going to want to do here is be able to send ANY arranger part, whether keyboard, style or SMF out to the module, have the master arranger select the tones in that module, while at the same time routing what needs to be played internally to it's normal destination. Few (if any) can manage this without you having to jump through hoops to achieve it, as basic as this is. Most of the time, you end up having to mess with the module as well, to set it up to receive some parts, whilst ignoring others, or other such dumb shenanigans. A remote is supposed to be just that... Remote. You are not supposed to have to touch it at all (f the master is designed properly)

And secondly... what's the thing most ARRANGER players would like to do with MIDI? Yep, that's right... Hook up two arrangers, and combine them into one über-arranger, with the strength of both combined.

This one, a no-brainer in my book, is the one thing they seem to go completely out of their way to ensure NEVER happens. The majority of even TOTL arrangers do not have codes to synchronize Fill selection, Variation selection, Breaks, Style selection, part mutes, even if you CAN hook them together and have them start and stop at the correct time And those that do, they are completely proprietary codes, with no standardization between manufacturers.

So, once again, despite those magical MIDI jacks actually being on the arranger, you can't do with them the most obvious things that one would consider they are there for...

None of this will change, until the arranger community as a whole starts to grumble, grouse and bitch and moan as often as you can, in as many places as you can, and show the manufacturers that putting these capabilities into an arranger would be worth their while... You might, for instance, point out to them that a feature designed specifically to hook two arrangers together is going to result in the sale of TWO ARRANGERS, not one!

And those that manufacture modules as well as arrangers (most of them) would benefit from increased module sales IF ONLY WE COULD USE THEM!

Beats me how they don't see these obvious facts, it really does...