I can't. Yes, it's a failure on me, but my experience is better without Facebook in my life.
You mention negativity, and that's part of it. I saw a steady stream of "the world's on fire" type posts. The other side, the rosy view of my friends and family also wasn't great. It was a steady stream of my brain using this as a chance to remind me I can't live up to these people, that I'm falling behind, and that in general, I suck.
It's not true. I could have crafted an equal fantasy and posted it, but I'm not that person. I could let the positive and negative posts go without influencing my mental well-being, but I'm apparently not that person.
All of this is a long way of saying, for me, Facebook is baggage I had to carry around with me. I didn't need to open it, but I knew it was there, ready to mock me at any time. Now my account is gone, and that bit of unnecessary baggage is gone. It added nothing to my life, only made it worse.