I haven't talked to Williams about his decision, but if he wants to play in the NFL then there's no better program in the country right now for receivers: Four first-round picks in the last two years. That's unprecedented for any position group from the same program in draft history.
A few things to keep in mind. One, Alabama wanted him. Saban wouldn't take him if he didn't think he could have a role.
Two, Ohio State threw to two receivers last year. Williams was on the field but the Buckeyes directed nearly 60% of their throws to two targets. And both are coming back this season. Maybe that's more of a reflection of Justin Fields' ability than Ryan Day's scheme, but unless you're one of those top two targets, it doesn't seem like you're going to get as many touches in that program. Bama has distributed the ball to more playmakers the last few years - and other than John Metchie will have to rely on new starters this fall. Bama has a couple elite talents at wideout expected to play big roles this year - go watch the spring game footage of Agiye Hall - but it looks like Williams might have less established traffic in front of him on the Bama depth chart.
I was told by someone close to Williams that Mizzou had a real shot at him. He has relationships with several players in the program. But I'm not sure how strongly he considered MU.