A report from PWInsider notes that all items pertaining to Sting that were once available on WWE Shop have been pulled as of Thursday.
No official reason has been given as to why Sting's merchandise is no longer available. However, in cases like this, it's generally a matter of WWE no longer being contractually bound to sell items for the talent in question.
In May 2020, it was revealed that Sting was no longer under contract with WWE. Around that same time, Mattel had pulled a Sting action figure from a planned Legends series.
Sting appeared in the WWE2K20 video game released in October 2019, but was not part of the Battlegrounds game released several months ago.
Sting last appeared for WWE in February 2019, as part of the 70th birthday celebration of Ric Flair during an episode of Monday Night Raw. His last match also came in WWE, against Seth Rollins at the 2015 Night of Champions pay-per-view. The match was notable for the then 56-year-old Sting suffering a significant spinal injury off of a turnbuckle power bomb.