Let's do a small calculation.  Take a medium-sized country in Europe, say, France.  About 60 million inhabitants.  If these 60 million people paid their taxes with bitcoin, then that would mean: 60 million transactions.  At a rate of 3 transactions per second, that would mean, 20 million seconds.  231 days of full blocks.  By the time your taxes are paid, using the FULL BLOCK CHAIN, you can almost start over again.

France only.

Go figure if the US citizens and the Russians started paying their taxes in bitcoin too.