What causes Safari to quit after launch?

Add-on anti-malware, add-on anti-virus, add-on cleaner apps, a file system corruption, a preferences corruption, a buggy extension, corrupt junk in a browser tab, all sorts of stuff can potentially cause problems.

Launch Safari while holding the shift key, and see if that clears this.

If that doesn’t work, boot into Safe Mode, then launch Safari with the shift key held again.