Thanks to @CybertronBeast
on Twitter, we have an interesting piece of info from the Hasbro Q&A at Fan Expo Canada 2019! A fan asked why the recent Walmart reissue of Optimus Prime lacked its trailer, and the answer was simple: the mold isn't in good enough shape to use anymore.
This isn't exactly a surprise to those of us who collect toys: the last time a full reissue of Optimus Prime was done was in 2012,
and is noted on the TFWiki as suffering from Mold Deterioration.
The short and sad answer is that everything wears down eventually, and as one of the most-reproduced Transformers Prime was an excellent candidate to see his tooling reach the end of its useful life.
The figure itself is probably in a better position to last longer, as a variety of alternate parts have been made for various safety regulations and collector purposes over the years. Smokestacks, fists, rifles... all of those will very likely outlast the core Optimus Prime mold, which of course predates even The Transformers
itself as a Diaclone transplant. All told we're doing pretty well, because we'd be willing to guarantee that this tooling was never intended to last almost forty years!
I think this was a great question to ask. There were a few likely reasons that the trailer was skipped, but because this tooling has been a key component to the origin and longevity of the brand, I see it as more important than asking a question about packaging that they are likely still determining. 10+ years from now, there will be interest in both answers, but I think the Convoy mold is far more important. Besides, it isn't a matter of one question over another. I would add, though, that with the many differences between later G1 Optimus Primes and the original Diaclone Convoy, I really wonder if the tooling was altered slightly that often along the way or if it was redone when Transformers originally boomed. When we saw images from TF Expo 2014, it didn't look like it ever had all 3 types of fists (and other variant details that would go along with those). It looked like it was altered from teh small original fists to the reissue raised cup fists.
Somebody wasted a question on this? It was probably the production mold that's unusable, if Hasbro wanted to they could've made a new one from the master mold but they probably didn't want to spend the money, daddy needs a new 911. The better question would've been how are people going to be able to see the figures in box if they're removing plastic windows?