Though I share your feelings somewhat - I was completely surprised by what you wrote in the comment higher up about iPhone gallery search. I didn't realize this is possible in a reliable fashion, much less off-line and deployed in a mass market device.

You know that some teens don't even save some images? They store them on specific instagram accounts they make for a specific category. My cousin had an instagram account for close friends (5 people) where she only shared bad things that happened to her during the day. Another one for nice things, etc. All those memories were recorded in app and never saved in the device, only stored as stories on the account. Guess what? She was sad a while ago because somehow she lost access to one of this accounts and so to all those pictures/videos.

Also the fact that some teens save a lot of pics on their devices doesn't mean much in the grand scheme of things. In 2008 I had folders upon folders of images downloaded from the internet. Now i'm not even sure where they are, probably in some hard drive in some closet. You can be sure that if i remember any of those contents I won't dig up my hard drive, but google them (use a comprehensive global search engine). We have no idea where all this collected data from teens will be in 15 years, it's not unlikely that it will be lost or archived in hard to reach places and forgotten. I've stumbled some times into "meme dumps" where they upload all their memes to a service to free space on their device/icloud.

For sure teens use technology in ways that might be unexpected and counter-intuitive to us, but I don't think that invalidates in the slightly the need of a global search engine for memes. It's a good idea if i want to find a meme that I saw, a need that I don't think will disappear anytime and that's also not a millennial+ only problem.