It wasn't Mohammed who founded Islam.

[Rayaan]

It also depends on when these claims were made. If they were made tens of years after Abd-Al-Malik's introduction of the madrassas and spreading of the religion, then... yeah... it is expected that many people will have the same basis, the same belief.

The claims were made both during and after Muhammad's death. These claims (about his Prophethood) were preserved in peoples' memories at first, and then were eventually written down about a hundred years later, starting from Ibn Ishaq's biographies. Many other corroborating information about Muhammad are recorded in Bukhari's hadiths which were compiled another hundred years later.

Nevertheless, the claims about it are abundant and they all unanimously refer to one and the same thing: the Prophetic role of Muhammad.

Errr... territory, land. That's the main usual suspect.
I'll just go ahead and take one more guess: maybe the land where his tribe was established became very poor and lacking in fauna and flora, perhaps the desert was creeping in... I don't know, I'd have to look it up. And they decided to take land from some other people who had decent land, decent food, decent animals.

Yeah, good job, keep the guesses coming. I find them absolutely enthralling.

Why do I think number 3 is more likely? Because, the earliest evidence of such a claim comes many years... decades, even... after his "agreed upon date of" death.

But at least the earliest evidences did arrive many years later. Better late than never, right? The evidence for your claim, on the other hand, that someone else attached Prophethood to Muhammad, doesn't came later, earlier, nor ever. You have no problem accepting that someone (totally unknown to you) falsely added a Prophetic role to Muhammad, while there are no writings at all to support that, let alone contemporary writings. And yet you have a problem believing that Muhammad claimed himself to be a Prophet, even though there are writings about such a claim being made, albeit many years later. I strongly find that to be more of an intellectual dishonesty than mere fallacious reasoning.

I highlighted the two parts of your quote for a reason. Why?

Because if you're going to judge what is more likely by the availability of evidence, then you have automatically refuted your own argument, since you, admittedly, have no evidence at all.

Way to be consistent.