This really isn't the grand insult you seem to take it as. It's a meme, not a 100% serious statement or comment about other people.

Aromantic people get told all the time all kinds of things, ranging from being called some emotionless machine just because they don't feel attracted to people romantically, to many other colorful insults I can't quite think of off the top of my head, and those are insults.

And neither is this saying any kind of relationship is bad or "weak" to have, there's different kinds of relationships, and they don't necessarily have to be romantic in nature to have deep meaning or connection to them.

In many cases those non-romantic relationships can mean more than a romantic one for some people, and in that way, it goes against what feels like the world telling everyone that you absolutely need a romantic relationship.

Edit: Nearly forgot to mention, but the broad generalization you made in the last sentence doesn't really apply either.

Not everyone within a category or group thinks or feels the same way. Some aromantic people decide they want to try romantic relationships anyway, despite the lack of basic attraction to it, the same way some Asexuals might decide to try sex despite the lack of sexual attraction, while others might avoid it entirely.