It was a concession granted in the early days of Islam, then we were later commanded to perform the full bath.
حدثنا محمد بن بشار حدثنا عثمان بن عمر أنبأنا يونس عن الزهري قال قال سهل بن سعد الساعدي أنبأنا
إنما كانت رخصة في أول الإسلام ثم أمرنا بالغسل بعد
[Sahih] Reported by Tirmidhi, in the Book of Purification, chapter on what has been said, "Water is required only from water," under no. 110, from the hadith of Yunus bin Yazid through this chain, and he said, hasan sahih.Zuhri was followed by Abu Hazim, as found in Abu Dawud, no. 215, and elsewhere, and Ibn Khuzayma, Ibn Hibban, Daraqutni, and Bayhaqi graded it sahih.