Because its been four days and they are all about the same size with two seed leaves and two small jagged leaves
Give them some time. They all are not created equal. Let them grow. 5 more days and you will see a change
I know the feeling you are having. Seedlings jump out of their shells with energy stored in the first two oval leaves. Then they have to get their roots established before they can start growing real leaves. All seedlings grow quickly for the first week then stall for a week. What you don't see is that the plant is growing twice as fast under the soil. Just give it some time. Hope this helps, -J