Why did the Muslims fix Quran as the last scripture and Muhammad as the last Prophet?

[Shri Anil asked: Abrogation (nullify/negate) of verses in Quran: Regarding the abrogation of verses Quran says the following: Quran 2:106: "We do not abrogate a verse or cause it to be forgotten except that We bring forth [one] better than it or similar to it. Do you not know that Allah is over all things competent?"

The application of above is regarding the drinking of alcohol, in which Quran adopts a graded approach, initially allowing drinking of alcohol but gradually advocate to completely stop its usage.

Quran 2:2:219, which allows but discourages Muslims from drinking alcohol; 4:43, which forbids Muslims from praying while drunk, and 5:90 which commands Muslims not to drink alcohol. These seemingly contradictory commands are explained by the first verse being abrogated by the second, and the second by the last, as part of a gradual process of preventing early Muslims from alcohol consumption. Thus, we see that Quran itself accepts a gradual revelation of truth and finally fix in the final truth.

Surprisingly, this approach is not followed in other aspects. If this concept is really followed then Muslims would have accepted other scriptures and other Prophets after Muhammad also. Swami, why they did not extend this concept in case of Quran and Prophet Muhammad? Why did they fix Quran as the last scripture and Muhammad as the last Prophet?]

Swami replied:-  I am responsible to explain about the original Prophets like Krishna, Jesus, Mohammad etc., and not responsible to explain the ignorant behaviour of their followers. I am not a blind total supporter of any religion and I am concerned with the scripture and the basic human incarnation of God in each religion.