To answer, this scholar's explanation of the Islamic view should be helpful.
"The writings of the Old Testament, the Gospels and the Epistles, all
represent vicarious experiences retold at second, third, or fourth
hand by their authors with an additional reworking by redactors and
editors. Within the New Testament are four Gospels, utterly
incomprehensible to Muslims, since the Gospel entrusted by God to
Jesus was reputedly a single Book. The conclusion derived by
Muslims is that because there are four, none of them are valid or
reliable. In fact, the popular Islamic explanation is that the
early Christian community lost the original Gospel received from Jesus
and set about to make good the deficiency, by substituting for one
sequential account an intricately woven fabric of writings and
traditions of many periods and different generations. Thus, according
to Muslims, the teachings of Jesus might now be irretrievably lost
to posterity were it not that their substance is reserved in the
Qur'an." Islam: the way of submission Solomon Nigosian (Crucible,
1987) last chapter, 'Islamic Understanding of Christianity' [Emphasis
mine].
That is truly surprising, given that there are only 25 verses in the entire Qur'an that speak of Jesus! The scholar goes on:
"Where there are differences or discrepancies between the biblical and
Qur'anic accounts, Muslims explain the biblical record as some form of
corruption. There is no better evidence of this than the words of the
eminent twentieth-century scholar Sayyid Amir Ali:
'It is an article of faith among Muslims of all shades of opinion that
the Christian Gospels in their present shape give an imperfect and
erroneous view of the life and preachings of Jesus, and that his
sayings have been garbled and tampered with according to the
idiosyncracies of individual compilers or the environments of the
times and the requirements of factions and sects.' A. Ali,
Christianity from the Islamic Standpoint, Hibbert Journal, Vol.iv, no.2 (Jan. 1906)
"...Muslims argue that Christians and Jews were not fit custodians of
their own Holy Books and that they tampered with them in various ways,
particularly by suppressing or obscuring what otherwise would have
confirmed Islam and the true nature and identity of the Qur'an. Stated
differently, the Islamic view is that the content of Christian
Scriptures does not match the content of the Qur'an; in their original
form they did match. The original form is irrecoverable and corruption
has occurred in the present versions." op. cit. Solomon Nigosian
p.195
That seems to make it perfectly clear, that the four gospel accounts in the Christian New Testament are disregarded and dismissed by Muslims as a fabrication, totally departed from the origin gospel which Islam claims came with Jesus - but is now lost. That also explains why Christians do not follow what Islam claims to be 'the gospel'.
