Single door is nicer bc you only have to open one door, the french doors you often have to open both bc they are too small to get to things unless it's in the door compartment. Opening or closing both doors with things in your hands gets old, and if you want to get into the meat drawer you have to open both sides fully then slide a huge tray out to get to it. Good luck opening one door and trying to squeeze a casserole dish in.
Single doors close somewhat automatically, might need a knee or hip nudge. French doors are more manual, closing each door individually. French doors often beeping bc they didn't get closed correctly. They have a little flap between the doors that gets worn out and loose, so that will also make it annoying to close.
Single doors open up out of the way, french doors always have one side flapping in the way making sure neither side of the counter can be used easily.
Single door type fridges are usually very simple, easy to fit a lot of stuff in them, french door fridges seem bloated, tons of wasted space.
French doors are more expensive and seen as a luxury item, despite single door fridges being common due to cost I think people perceive french doors to be an upgrade, but imo it is a downgrade, thus unpopular.