First of all, according to the text in Daniel itself, it was written around 530 BCE. That is a far cry from the 165 BCE date claimed by this article. Whilst there are good reasons for landing on the earlier date, scholars who don't actually believe the bible prefer the later date for Daniel. That is because it would put Daniel's book after the main events it prophesies about. That means Daniel was not writing prophecy, but simply recording history, pretending it was originally a prophecy. Many modern scholars like this because it removes the supernatural element from Daniel.
The Wiki author says this view is the 'consensus of modern scholarship'. Understand that 'modern scholarship' is not referring primarily to bible-believing scholars, but those who study the bible as a piece of ancient literature, usually saying it is a mixture of myths and history. They are secular scholars, often not even believing that God exists. They study the bible and other ancient texts for their literary and cultural value. It is therefore not surprising that the later date for Daniel -- the date that essentially makes the book out to be fake -- finds a lot of acceptance amongst 'modern scholars'.
Regarding the apparently failed prophecies of Daniel mentioned here, those prophecies have not failed. As you might know, when it comes to biblical prophecy, there are often different interpretive theories (the book of Revelation is a prime example). In this case, this article has chosen an interpretation that does not fit the data in Daniel.
This is where the intentions of the author (that is, of 'modern scholars') shines through. Instead of presenting other options which do work for Daniel's prophecy, the Wiki author sticks to this failed interpretation, and leverages it to claim support for his erroneous dating of Daniel.
The author's argument is false. Daniel's prophecy was referring to the Roman Emperor, not the Syrians, and in this the prophecy works simply. Daniel spoke the plain truth, and there's no reason to doubt that the book was written when it says it was, in the 6th century BCE. That, of course, would not be discussed or admitted in an article on Wikipedia, because it gives too much legitimacy to the bible, and particularly to Divine realities.