Mandrew wrote on Today, 08:43:

This one was originally paired with the Tulip AT compact and that shipped with both the MDA and the CGA option. I've yet to see a MDA card with a 6DIN connector but this has the original 6DIN-9pin cable included.

CharlieFoxtrot wrote on Today, 08:29:

Why did they use other type of connector? Most likely those monitors were also sold for other applications, such as bundled with some terminal

Good explanation, the same chassis was probably sold to multiple manufacturers based on application and the 6DIN connector was cost effective.

Yes, I saw that it was Tulip branded tube, but it is pretty much certain that it isn’t manufactured by them. As an european computer brand I can almost bet that the monitor is manufactured by Philips and nearly identical to what I disucssed, at best with some slight modifications in addition to the different badge. If I remember correctly, some of those Philips monitors had a fixed cable with 6-pin connector, but monitor was supplied with an adapter for PC-standard 9-pin. It is a simple and cheap solution when the monitor uses correct signaling, just a rewire.

The monitor was probably originally aimed towards some specific application, maybe a Philips made terminal or something. For other purposes they just supplied an adapter or specific cable as that doesn’t require any big changes in the chassis assembly line. So yes, cost optimization is the reason for this type of stuff, as it is pretty much always with choices regarding large scale manufacturing.