Only in your rather biased opinion: we have no problem whatever accepting both of them!
Again, we disagree; and our scriptures make the legitimacy and God-sent nature of the various religions quite clear! I quote:
"There can be no doubt whatever that the peoples of the world, of whatever race or religion, derive their inspiration from one heavenly Source, and are the subjects of one God. The difference between the ordinances under which they abide should be attributed to the varying requirements and exigencies of the age in which they were revealed. All of them, except a few which are the outcome of human perversity, were ordained of God, and are a reflection of His Will and Purpose. Arise and, armed with the power of faith, shatter to pieces the gods of your vain imaginings, the sowers of dissension amongst you. Cleave unto that which draweth you together and uniteth you."
(Gleanings, CXI, pp. 217-8)
Bruce