Why do they call massachusetts common wealth?

something like that

In the era leading to 1780, a popular term for a whole body of people constituting a nation or state (the body politic) was the word "Commonwealth." This term was the preferred usage of some political writers. There also may have been some anti-monarchial sentiment in using the word commonwealth. John Adams utilized this term when framing the Massachusetts Constitution.

Adams wrote: "There is, however, a peculiar sense in which the words republic, commonwealth, popular state, are used by English and French writers, who mean by them a democracy, a government in one centre, and that centre a single assembly, chosen at stated periods by the people and invested with the whole sovereignty, the whole legislative, executive and judicial power to be included in a body or by committees as they shall think proper." (John Adams. Life and Works, vol. 5, p. 454)

In its loosest form, commonwealth means for the common or public good, and is often a state formed for the common good of the people.

The commonwealth designation is important to Massachusetts, Kentucky, Virginia and Pennsylvania, as these states originally defined their governance in direct opposition to the governance of the British Empire. The designation now lacks meaning and has merely been retained as a salute to the past history of rebellion that freed the US from British rule.

These are both true another important thing to know is that a big part of being a commonwealth then (not so sure now) was that they help public town meetings in which the public could attend and make comments and they still do today as far as i know.