Fountainpens are not the most practical writing instruments. Probably the least pracical out there.
You need to clean them, refill them, sometimes they leak etc.
I guess most people who are into fountain pens, either bought one or tried it at some point. And really liked either the feeling of writing with it or how their writing looked when using it. Or usually a combination of the two.
What I love about them is a complicated one
First of all I love the tactical feeling for writing with one
Second, I love how much more personality your writing have with a fountain pen nib than a regular pen.
Third I love how you can find more or less any color you want for it
Fourth I love how many pens and nibs there are to pick from. You can literally find anything. Everything from very inexpensive to very expensive.