"hmmm... seems like the government wants to tax everything" this is not far from the truth, but Government only taxes things that seem to be pulling in a lot of profit. This means that downloads are bringing in a massive profit with no payment to the government making it easy money therefore encouraging everyone to do it.
Downloads can be legal (those that are often registered and charge a certain amount) and illegal (random, FREE and very enticing), if government suggest tax on both (more especially illegal aspect) they would be condoning piracy and all the other crimes associated with downloads, thus making the tax paid somewhat of a bribe.
Giving Government the permission to tax downloads would also in a way, give them permission or the right to control and regulate what is downloaded, this complicates matters even further as they begin to control the type of media information we can receive. Another disadvantage would be the privacy of downloading as Government would have access to who does what, when, why, how and where.
On the other hand, the tax money can go towards improving areas that lack proper technological advancement such as government websites and the proper maintenance of such. This would mean meeting the proper standards when it comes to websites and may even be able to develop software that prevents illegal downloads therefore reducing piracy.