Henry claimed that they were dissolved because of their corruption. Commissioners visited monasteries and wrote unfavourable reports, known as the comperta, to Cromwell. Reports were clearly exaggerated but Henry probably believed them.
Government claimed that corrupt monasteries could be put to better use as colleges, schools or hospitals. Many reformers including many of the Commonwealth Men agreed.
Real reason was the monastic wealth that Henry coveted, as he was in financial difficulties and feared a joint invasion of England by France and Spain.
In 1535, Cromwell's agents carried a special survey to find out the accumulated wealth and income of secular as well as regular (monastic) foundations.
This report was called the Valor Ecclesiasticus. It certainly showed Henry how wealthy the Church was.
Henry wanted to be seen exercising his Headship of the Church as a reforming monarch.
Cromwell was against monasticism; he believed that monasteries were dens of superstition and pro Papal sentiment.
At a time when the government was worried about opposition, it was thought that they might be centres of disaffection.