What are the underlying factors driving their popularity?
Memes are popular jokes or characters in social media. These memes are usually very popular among communities since they are usually inside jokes. Because of strong community, these memecoins usually become successful. Though it should be noted that since they are practically created due to memes, there is no really real purpose behind which makes them driven by hype alone.
You are 100% right that community is the important figure here. I mean we are talking about tokens who build a community first via the meme world, they meme it and people who love that meme and use it end up being the community of it and THEN they make a token of it which means that when the token starts there is a community to hype it already so they do not have hard time marketing it.
However, we need to remember that there are thousands of them stealing from each other too, like how Ape ended up big right, and Doge was always big, and Pepe became big these are all valid, I wouldn't invest into them but they are valid, but then what happened? Someone made Apepe, or DogeApe, or Dogepepe whatever, these type of shitty tokens end up not being that great, which is an issue and I think we need to be careful with those ones, because most of the time they are not looking like they are going to be profitable and yet there are people invest into these.