Why Isa had no father like everybody else?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Allah created Aadam without a father or a mother, then He created his wife Eve from a father (from Aadam himself) but without a mother, and then He created ‘Eesa (Jesus) from a mother but without a father, and He created all other people from a father and a mother. All this, to show His Great Might and that He is Omnipotent and Capable of everything.

Muhammad Al-Amin Ash-Shanqeeti, said in his Tafseer (interpretation of the Quran) Adhwaa’ Al-Bayaan:

"The Saying of Allah (which means): {…and We will make him a sign to the people and a mercy from Us. And it is a matter [already] decreed.} [Quran 19:21], Allah mentioned in this verse: that among the wisdom of the creation of Jesus from a woman without a husband, is to make that a sign for the people, i.e. a sign that indicates His Perfect Might, and that Exalted be He creates what He wishes as He wishes. If He so Wills, He creates him from a female without a male as He did with Jesus, and if He so Wills, He creates from a male without a female, as He did with Eve, as in His Saying (which means): {…and created from it its mate.} [Quran 4:1]; meaning that He created from that soul, which was Aadam, its mate Eve. In addition, if He Wills, He creates without a male and without a female as He did with Aadam, and if He Wills, He creates from a male and a female, as He did with all the offspring of Aadam. So Glorified and Exalted be He, Who is over everything Omnipotent. What Allah mentioned in this verse, that He made ‘Eesa a sign, as his mother gave birth to him without a husband, He pointed to this as well in Chapter 21, as He Says (what means): {...and We made her and her son a sign for the worlds.} [Quran 21 91]; and His Saying: {And We made the son of Mary and his mother a sign.} [Quran 23:50]." [End of quote]

For more benefit, please refer to Fataawa 1894 and 91339.

Allah knows best.