When prayer time is approaching, rushing through ablution can defeat the purpose of preparing correctly. Speed and carelessness are not the same: someone may wash properly in a short time, while another may leave dry areas through inattention.
In وَهُمْ عِجَالٌ, هُمْ refers to those making ablution and عِجَالٌ describes their condition. The wording identifies the haste that contributed to the problem.
For example, a person may wash the feet but fail to check whether water reached the heels. The right response is attentive washing—not obsessive repetition based on unsupported doubts.