And you source for this is?
Mark:
“Nothing in the Gospel identifies its author by name, since the label “according to Mark” was added later.”
Daniel J. Harrington, S.J. “Introduction to the Gospel of Mark,”
New Jerome Biblical Commentary, Prentice Hall, Inc., New Jersey, 1990, pg.596 (section 2)
Mathew:
“The Gospel early acquired prestige non only because of its intrinsic merits (e.g. the Sermon on the Mount, chaps. 5-7) but because it bore the name of an apostle (mentioned 9:9; 10:3). But, since the author of the final Gk text seems to have copied with modifications the whole Gospel of Mark, it is now commonly thought that it is improbable that in its present form it is the work of an eyewitness apostle.”
Benedict T. Viviano, O.P., “Introduction to the Gospel of Matthew,”
New Jerome Biblical Commentary, Prentice Hall, Inc., New Jersey, 1990, pg. 630 (section 2)
Luke:
Luke was a companion of Paul and not an eyewitness to the life of Jesus. I’m surprised you didn’t know that. Source: the Bible.
John:
“The ‘writing down’ of the Johannine traditions was clearly part of the ongoing life of the community. It may have been the result of a ‘Johannine school’ of disciples of the Beloved Disciple and teachers within the Johannin churches. There is sufficient unity in the literary composition and the narrated point of view in the Gospel to justify the claim that a single individual was responsible for the structure of the gospel narrative. But the importance of the community’s history of faith in shaping the Johannine tradition makes preoccupation with a single Johannine author inappropriate today…”
“…Finally, modern exegetes observe that the developments in christology and the realized eschatology of the Fourth Gospel are well beyond what would be likely for a Galilean fisherman.”
Pheme Perkins, “Introduction to the Gospel According to John,”
New Jerome Biblical Commentary, Prentice Hall, New Jersey, 1990, pg. 946 (section 12)
In case you were wondering, The New Jerome Biblical Commentary (where I sourced this information) is an authoritative compendium of modern biblical scholarship of the community of Roman Catholic sholars. It bears the Nihil Obstat of the following:
Raymond E. Brown, S.S.
Joseph A. Fitzmyer, S.J.
Roland E. Murphy, O.Carm
Censores Deputati (not sure what this latin phrase means, but I include it for anyone who cares)
And it bears the Imprimatur of
Reverend William J. Kane
Vicar General for the Archdiocese of Washington, November 15, 1988
So to re-cap - these are
Catholic Scholars writing with the
Approval of the Church presenting
current scholarly information about the
authorship of the Gospels. You are of course free to have your own opinions, no matter how uninformed they may be.