Islam is astonishingly insecure about its origins, which speaks volumes. Historians constantly delve into the origins of Christianity and it's been extensively researched and critiqued on many levels. A historian
dares to question Islam and receives death threats.
Makes you wonder how many Muslims do actually believe in their religion with complete confidence and faith if they are so insecure that the merest questioning of the historical accuracy of their scripture makes them start handing out threats.
Most Christians and indeed followers of every other major religion accept that their scripture isn't, for want of a better word, gospel, but is largely parable. The sooner Islam, the youngest of the major religions it should be noted, joins the grown ups, the better.
Right now it comes across as a petulant, insecure teenager.
As far as it having run for 1400 years goes, well, so what?
Look at
Joseph Smith.
Much more reliable historical information, wanted fraudster, people adhere to his religion and it's growing pretty rapidly.
Or even more recent
L Ron Hubbard. Founds a religion basically for a bet, it's worldwide, influential, and growing.
Some people appear willing to believe any old bollocks. Islam happened to have had a millennium and a bit head start and is more aggressively expansionist.