At this point I think governments are just giving their citizens a lot of options to pay their taxes in hopes of actually collecting taxes from the public. They are not doing this to 'revolutionize' or 'modernize' their payment system, because if they wanted to they'd be starting with improving their online payments first. They probably found out that people are interested in actually paying their taxes if there are other ways of doing so. Cryptocurrencies are something that is more plausible for this goal since people would be interested in trying it out. Also, they can profit off of these payments if they timed their conversions right.
I'm not sold that this is done for the 'betterment' of the system.
Except for a few exceptions we need to always assume that whatever a politician does is always done with only one idea in mind, which is to benefit themselves, they do not really care about their citizens at all but they do care about keeping their privileges, and with this in mind there are two main reasons why I think they may have done something like that, cryptocurrencies are popular at Argentina due to the awful economic management of the government so they are trying to obtain some kind of foreign currency even if indirectly, while the second reason is the one that you state as they are trying to invite people to pay their taxes while at the same time they are trying to identify as well the people that use cryptocurrencies in their country. I'm not sold that this is done for the 'betterment' of the system.
