A kind of flattery, one would say.
I've been noticing something lately... and it's happening enough with people I've worked with in recent history, that I feel like I have to make note of it.
So, it's not outright stealing, at all. I get that the people who commissioned these were probably like, "hey, make it look like this poster" and that was executed. A younger me would probably react in an uncouth manner, and to be honest my heart still sinks a little when I see things that may or may not be influenced by something I've created.