I make my database first, in yet to change anything, So in a way migrations aren’t only for making data?

And then what if the next day, you realized that you needed to add a new table to your database?
And then the next day, that you need to drop a column from an existing table?
Pretty soon, you've made all kinds of changes and the only thing you can really do is say, "Just forget all those other changes... use this latest file!"
Not a very good way to handle it.
And then imagine if your co-developers had their own changes that they needed to make somewhere in between yours.
There's just no way to stay organized when approaching the problem that way.
Migrations solve all of those problems.