Probably because the polemic that 'Henry the VIII founded the Church of England' is also a gross-oversimplification, and false at that.
To begin with, the Church of England was a continuation of the local Catholic dioceses of England. This is why the Catholic hierarchy have no Archbishop of London, nor of York, or Lincoln. Those three sees were lost to the Roman church by the schism of those bodies (note, schism - not 'creation of new church'.) The worship of the Church of England during Henry VIII's rule was the Sarum use of the Roman rite, with commemorations of the Pope removed, as well as commemorations of more recent saints. Even with the 1st Book of Common Prayer (1549) the liturgy was considered a Catholic rite by Rome - it was not until the Ordinal was changed that Rome changed its views on the matter. The 2nd Prayer Book was the first Protestant book, but was never accepted by the Church of England - it was promoted for a few months in one year by the Government, but never became widespread. It was not until the rule of Queen Elizabeth the I of England that they had a fully Protestant liturgy, and final schism with Rome.
However, those bishops during the reign of Elizabeth I, Henry VIII, and Edward VI did not look to Henry VIII as the founder - but to the local history of their church. In fact, the English church had a long history of considering their local church independent of Rome. The Witenagamot - the Anglo-Saxon 'parliament' of England forbade appeals to Rome in AD 690, then again in AD 747 where Canterbury was considered as the Primate of the Church in England (it had moved successively from Gloucester/Glastonbury, to London, to Caerleon, to Menevia, to Canterbury.)
As for the founding with St. Joseph of Arimathea and St. Aristibule, and the conversion of Bran the Blessed - it is asserted by Welsh tradition, such as Rhigyfarch (who asserted the independence of the See of Menevia from the Norman See of Canterbury.) Rome itself and its bishops accepted the claim at the Councils of Pisa, Constance, Sienna and Basle - all during the 15th c., only a century before the Henrician Schism (note, that is the historical name of Henry VIII's schism - the Henrician Schism, not the 'Founding of the Church of England'.)
Personally, I'm a little protective of Continuing Anglicans and Old Catholics - many of their clergy, laity, and even hierarchs are 'almost Orthodox'. There is a bit of diversity with Continuing Anglicans, but they do tend to preserve much of their various Anglican traditions that the TEC has willingly sloughed off. Yet, you will find some in TEC or the Anglican Communion that will not claim Henry VIII to have 'started' any Church, but to have reasserted a perennial claim of the Church in the Isles - that 'the buck stops here', and that their church has Apostolic origins. And they should - as such is correct: we Orthodox know it, Rome knows it, etc.