Imgflip was always popular for its tools, not its community.
The site started to grow rapidly in the community aspect during the pandemic, because people were looking to make memes. Some of these people got interested in the community side of Imgflip, mostly young, and then stayed afterwards, which explains why Imgflip stayed popular well into 2021-22.
But then, those young kids started growing up. Iceu himself, for instance, told someone that he joined when he was underaged. If I remember it correctly (I probably don't), he was 12. Now, he's probably 17, and could possibly even become 18 this year, depending on his birthdate. An 18-year old will absolutely have no time for Imgflip if they want to start a good career.
But I don't think Imgflip's tools will die anytime soon; even Elon Musk uses them:
https://xcancel.com/dylanwenzlau/status/1757600260757803320
It's just Imgflip's community that I don't think will sustain for too long. I once discussed in a now-deleted conversation with Imgflip developer 'acuity12' about the possibility of ending Imgflip's community altogether, and instead focusing on professional tools alongside the Meme Generator and GIF Maker, which was more profitable in both of our views, though I now see it as extreme.
He actually hinted at the possibility of adding more professional focus, and removing much of the community aspects like streams, while keeping the more casual tools llike the Meme Gen. and the GIF Maker, because he said it would not onty bring more money from subscriptions, but also save up a lot of moderation money, and bring more advertising revenue because there will be no NSFW content to discourage advertisers.
