I have seen it in many new designs.
Kids will say "Joe is allowed to do this, why am I not". The fact that something is done by someone, does not prove it right.

I worked with an engineer that was mired in the past, he actually insisted on using a 8032 for an app requiring about 2k of code memory. When asked why not an internal memory variant, the answer was "that is not how it is done". So by the reasoning I have seen it in many new designs. it can equally well be stated "there is no reason, whatsoever to use an internal memory variant"

But why manufacturing then a radiation hard variant if the 8255 seems to have no future?
I'm sure the "variant" was developed in the days when it was thought that the 8255 "had a future". If you have everything needed to make simething and somebody is willing to buy it, why refuse?

Erik