Governments can easily legalize bitcoin by passing a law, but I think it would be difficult for them to control bitcoin transacctions since bitcoin is anonymous. For users it would be clarifying in order to change bitcoin to fiat, but if the network can function by itself and make transacctions p2p I don't see what the role of states will be and what justification they can invent to tax activities.
Actually this is main reason. Governments know better what the advantages bitcoin is carrying along are but they only waiting for the time that may be in upcoming future bitcoins feature i.e. decentralized would be changed and all these governments can control the yes and no of bitcoin. But we hope a time come in near future when all this happens and we would be enjoying the perks.
you also have a point, and it seems that it is actually true, but it could be no also. the big participation of the government and the most positive way to help bitcoin grow is by legalizing and actually accepting it as another method of payment, but as usual it will take too long before it will happen, besides there are lots of hindrances before they can pass a law and start to debate if it will be finalized or not.
The legalization of the bitcoin depend on the government, they can legalize it but they have already great deals with banks and banks does not like the bitcoin. Because bitcoin is useful for a common people , therefor people are now going toward bitcoin, By this banks are against of bitcoins. Due to the banks the government also slow in the process to make the bitcoin is a legal currency.