Why did the poll tax stick around so long in Massachusetts? Mainly because in the early years it was a major source of revenue for the commonwealth (roughly 30%) and in later years was still not insignificant and its repeal would have cost the state a chunk of change the state didn’t want to have to replace. While it’s unlikely by the 1960s most people thought a poll tax was a good idea, few leaders wanted to make the tough decision to repeal it – even if the rate had been fixed at $2 for several years. Only in 1964 did they repeal it in advance of passage of the constitutional amendment.

The poll tax would be prohibited the following year nationally under a constitutional amendment. https://www.daileyint.com/mytimes/lkback3.htm