Just speaking for myself but I liked being able to just open Facebook when I want to look at Facebook. That goes for PMs people send me on Facebook.

I didn't want a second app running at all times in the background when my goal was to minimize Facebook usage when possible.

Now I have to jump through hoops to check messages every once in a while on my phone because they make it so they won't show up on mobile unless you install their secondary app or switch to a desktop user agent.

So now I just check messages once or twice a week on desktop and use their service even less often.