It might be amusing to take the viewpoint of the fictitious average office worker who would never dream of using a fountain pen (heaven forfend!) and probably has little idea of what one is, beyond the notion that it involves a bottle of ink, a thing that is a catastrophic accident waiting to happen, for the clumsy among us.
The other things he may have heard are that fountain pens are prone to leaking and also supplying blots, especially at the bottom of a page of otherwise blameless text. Unlike the reliable and trustworthy Crystal Bic, the fountain pen cannot be casually cast aside but must be capped and laid down gently. How inconvenient!
The fact that the fountain pen is not held at the wrist-wrenching angle of the ballpoint is unknown to him and would not be understood if it were to be brought to his attention. Line variation is neither here nor there. If the ballpoint doesn’t do it, it’s of no consequence. In any case, if you want to be fancy there are gel pens and nylon tips. No need to be fussing with the inconvenience of a fountain pen.
Of course all of the above is myth rather than fact or generalisation from an occasional incident but I’m sure they are commonly-held beliefs.
The dear old queen is gone from us. She used a fountain pen to sign documents and there has been much discussion about which fountain pen she used. I imagine she had all the fountain pens she might have wanted and used whatever came to hand. Her father had a fondness for Wyverns and used a couple of crocodile-skin-covered ones. And what of King Charles III? Is he a fountain pen user? Time will tell.