My facebook ad reach is ridiculously low.

My facebook ad (video views) has been running for 4+ hours now and the reach is 3 !! Despite that my potential reach is 1m.

Why is that?

You should start A/B testing to get better result. FB is really strict now....

Perhaps it is the competition around the community that you target and how much you are willing to pay Facebook. If there are advertisers who bid for more money, their ads will get priority over yours.
If you can afford it, try to increase your bid.