steam is not launching on my mac

when I try and open steam on my Mac it doesn't open. the icon flashes a bit on the applications bar at the bottom of the screen and then vanishes.

I have gone to steam support for help but its useless, nothing comes up for help.

this has been going on for over a year and I can't figure out what to do. I have tried reinstalling steam, restarting my Mac and deleting files.

any advice or reasoning??