You do realize of course that in Poser format using the material room is the "correct" way of offering MATs?  That creating Pose Library MAT files was a hack done during the Poser 4 era and has really been outdated since P5?  Heck I recall a time when many placed those MAT files in the Camera library because they were trying to cut down on how long the library listing was getting as it only saw xx number of folders.

In general perhaps vendors create Pose Library MAT files because A. The customers prefer it as they are used to it, and B. Perhaps they are too lazy to bother opening the Material room Tab.  Personally I work from inside the material room so it's irrelevant to me.

There are also items, props particularly, that can't use a Poser library MAT file.

As for using in a different software, that's great, but unless the product states it's compatible in something other than Poser then why are you expecting it to have or use outdated Poser hacks? 

A quick peek at the readme is in fact quite reasonable, and generally the file listing is at the bottom of the readme.  While I mark my products if they use the Material room (props), many don't simply because using the Material room is the correct way of handling it.

Lastly, if you are going to be snarky and rude you have to expect the same back or no response. To you to respond in a condescending manner to those responding to you is just flat out rude and implies that you simply feel you know best on the subject, which frankly makes your opening question rhetorical.

It may be an old saying but it's still true that you "catch more flies with honey."

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