It needs to be low, but positive and keept stable. If it’s to high it will be self sustaining and increasing, if it’s negative everything stalls. 2% seems to fit the bill.
There could be an argument that 4% would have been just as good, and had the rest of the world united on 4% it would*. However, it would not have changed anything in last year’s combat of inflation. The target would have been defended just as fiercely causing just as much collateral. Only the numbers would have been slightly different.
*Ignoring for a bit those countries that has had to fight to keep inflation up.