If it actually is, there are four possibilities
1. the updates
the updates made users frustrated like the new home page, Many users are complaining about when you can just literally go back by clicking on streams. Another thing might be the fact that Dylan is giving different updates instead of what we wanted
2. boredom/lost interest in the Imgflip community
Users might not find some memes funny anymore so they might abandon their account or delete it.
Speaking of deleting their account, the third possibility is being forced to delete their account by parents. you may have heard about S.T.R.I.K.E having to delete his account by his parents, and ik you might be thinking, "Fernandope what makes you say that?" well when i was using Imgflip underaged (i never made an account when i first heard about the tos and the underaged_users stream) there was a top meme that had the "so long, partner" meme about someone named Raydog (not the big user) saying he/she is forced to delete Imgflip and gave his/her gmail to keep in touch. some might be announced while some might be unofficial
4. Users need to move on
Some users need to end their journey on imgflip someday... including me. I may be 13 but when i age, i must move on to the next chapter of my life such as finding a job, getting a car, buying a house, you know. i might need to be inactive for many reasons