Not only was Rhode Island the only colony/state to decline to send a representative to the Constitutional Convention of 1787, it was also the last of the newly-established states to sign and ratify the document that emerged out of those proceedings. As the document linked below illustrates, Rhode Island stood out among the already-fractious political entities for its staunch adherence to the Articles of Confederation, which strictly limited the powers of a central government, one of the most contentious issues debated at the convention and in political gatherings preceding it.
The direction in which the independent states were heading was strongly suggested by the known positions of many of the most prominent members of the pro-independence movement. Rhode Island's leading officials understood this, and they remained opposed to that direction--in effect, the movement towards a coalition of states bound by a strong central government. Any movement towards greater centralized control of the emerging country was bound to elicit demonstrations of annoyance from the citizens of that particular state. Rhode Islanders relished their reputation for independent thought and governance--a sentiment that had earned it the moniker "Rogues Island" more than a century before. The decision to boycott the Constitutional Convention, therefore, was entirely consistent with the colony/state's history, including its early opposition to the British Crown. Rhode Islanders simply rejected the notion of governance from outside their very limited borders, and did not want to give their imprimatur to the constitution that would emerge.